path: root/lib/setenv.c

/* Copyright (C) 1992, 1995-2003, 2005-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   This file 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.

   This file 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */

#if !_LIBC
/* Don't use __attribute__ __nonnull__ in this compilation unit.  Otherwise gcc
   optimizes away the name == NULL test below.  */
# define _GL_ARG_NONNULL(params)

# define _GL_USE_STDLIB_ALLOC 1
# include <config.h>
#endif

#include <alloca.h>

/* Specification.  */
#include <stdlib.h>

#include <errno.h>
#ifndef __set_errno
# define __set_errno(ev) ((errno) = (ev))
#endif

#include <string.h>
#if _LIBC || HAVE_UNISTD_H
# include <unistd.h>
#endif

#if !_LIBC
# include "malloca.h"
#endif

#if _LIBC || !HAVE_SETENV

#if !_LIBC
# define __environ      environ
#endif

#if _LIBC
/* This lock protects against simultaneous modifications of 'environ'.  */
# include <bits/libc-lock.h>
__libc_lock_define_initialized (static, envlock)
# define LOCK   __libc_lock_lock (envlock)
# define UNLOCK __libc_lock_unlock (envlock)
#else
# define LOCK
# define UNLOCK
#endif

/* In the GNU C library we must keep the namespace clean.  */
#ifdef _LIBC
# define setenv __setenv
# define clearenv __clearenv
# define tfind __tfind
# define tsearch __tsearch
#endif

/* In the GNU C library implementation we try to be more clever and
   allow arbitrarily many changes of the environment given that the used
   values are from a small set.  Outside glibc this will eat up all
   memory after a while.  */
#if defined _LIBC || (defined HAVE_SEARCH_H && defined HAVE_TSEARCH \
                      && (defined __GNUC__ || defined __clang__))
# define USE_TSEARCH    1
# include <search.h>
typedef int (*compar_fn_t) (const void *, const void *);

/* This is a pointer to the root of the search tree with the known
   values.  */
static void *known_values;

# define KNOWN_VALUE(Str) \
  ({                                                                          \
    void *value = tfind (Str, &known_values, (compar_fn_t) strcmp);           \
    value != NULL ? *(char **) value : NULL;                                  \
  })
# define STORE_VALUE(Str) \
  tsearch (Str, &known_values, (compar_fn_t) strcmp)

#else
# undef USE_TSEARCH

# define KNOWN_VALUE(Str) NULL
# define STORE_VALUE(Str) do { } while (0)

#endif


/* If this variable is not a null pointer we allocated the current
   environment.  */
static char **last_environ;


/* This function is used by 'setenv' and 'putenv'.  The difference between
   the two functions is that for the former must create a new string which
   is then placed in the environment, while the argument of 'putenv'
   must be used directly.  This is all complicated by the fact that we try
   to reuse values once generated for a 'setenv' call since we can never
   free the strings.  */
int
__add_to_environ (const char *name, const char *value, const char *combined,
                  int replace)
{
  char **ep;
  size_t size;
  const size_t namelen = strlen (name);
  const size_t vallen = value != NULL ? strlen (value) + 1 : 0;

  LOCK;

  /* We have to get the pointer now that we have the lock and not earlier
     since another thread might have created a new environment.  */
  ep = __environ;

  size = 0;
  if (ep != NULL)
    {
      for (; *ep != NULL; ++ep)
        if (!strncmp (*ep, name, namelen) && (*ep)[namelen] == '=')
          break;
        else
          ++size;
    }

  if (ep == NULL || *ep == NULL)
    {
      char **new_environ;
#ifdef USE_TSEARCH
      char *new_value;
#endif

      /* We allocated this space; we can extend it.  */
      new_environ =
        (char **) (last_environ == NULL
                   ? malloc ((size + 2) * sizeof (char *))
                   : realloc (last_environ, (size + 2) * sizeof (char *)));
      if (new_environ == NULL)
        {
          /* It's easier to set errno to ENOMEM than to rely on the
             'malloc-posix' and 'realloc-posix' gnulib modules.  */
          __set_errno (ENOMEM);
          UNLOCK;
          return -1;
        }

      /* If the whole entry is given add it.  */
      if (combined != NULL)
        /* We must not add the string to the search tree since it belongs
           to the user.  */
        new_environ[size] = (char *) combined;
      else
        {
          /* See whether the value is already known.  */
#ifdef USE_TSEARCH
# ifdef _LIBC
          new_value = (char *) alloca (namelen + 1 + vallen);
          __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
                     value, vallen);
# else
          new_value = (char *) malloca (namelen + 1 + vallen);
          if (new_value == NULL)
            {
              __set_errno (ENOMEM);
              UNLOCK;
              return -1;
            }
          memcpy (new_value, name, namelen);
          new_value[namelen] = '=';
          memcpy (&new_value[namelen + 1], value, vallen);
# endif

          new_environ[size] = KNOWN_VALUE (new_value);
          if (new_environ[size] == NULL)
#endif
            {
              new_environ[size] = (char *) malloc (namelen + 1 + vallen);
              if (new_environ[size] == NULL)
                {
#if defined USE_TSEARCH && !defined _LIBC
                  freea (new_value);
#endif
                  __set_errno (ENOMEM);
                  UNLOCK;
                  return -1;
                }

#ifdef USE_TSEARCH
              memcpy (new_environ[size], new_value, namelen + 1 + vallen);
#else
              memcpy (new_environ[size], name, namelen);
              new_environ[size][namelen] = '=';
              memcpy (&new_environ[size][namelen + 1], value, vallen);
#endif
              /* And save the value now.  We cannot do this when we remove
                 the string since then we cannot decide whether it is a
                 user string or not.  */
              STORE_VALUE (new_environ[size]);
            }
#if defined USE_TSEARCH && !defined _LIBC
          freea (new_value);
#endif
        }

      if (__environ != last_environ)
        memcpy ((char *) new_environ, (char *) __environ,
                size * sizeof (char *));

      new_environ[size + 1] = NULL;

      last_environ = __environ = new_environ;
    }
  else if (replace)
    {
      char *np;

      /* Use the user string if given.  */
      if (combined != NULL)
        np = (char *) combined;
      else
        {
#ifdef USE_TSEARCH
          char *new_value;
# ifdef _LIBC
          new_value = alloca (namelen + 1 + vallen);
          __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
                     value, vallen);
# else
          new_value = malloca (namelen + 1 + vallen);
          if (new_value == NULL)
            {
              __set_errno (ENOMEM);
              UNLOCK;
              return -1;
            }
          memcpy (new_value, name, namelen);
          new_value[namelen] = '=';
          memcpy (&new_value[namelen + 1], value, vallen);
# endif

          np = KNOWN_VALUE (new_value);
          if (np == NULL)
#endif
            {
              np = (char *) malloc (namelen + 1 + vallen);
              if (np == NULL)
                {
#if defined USE_TSEARCH && !defined _LIBC
                  freea (new_value);
#endif
                  __set_errno (ENOMEM);
                  UNLOCK;
                  return -1;
                }

#ifdef USE_TSEARCH
              memcpy (np, new_value, namelen + 1 + vallen);
#else
              memcpy (np, name, namelen);
              np[namelen] = '=';
              memcpy (&np[namelen + 1], value, vallen);
#endif
              /* And remember the value.  */
              STORE_VALUE (np);
            }
#if defined USE_TSEARCH && !defined _LIBC
          freea (new_value);
#endif
        }

      *ep = np;
    }

  UNLOCK;

  return 0;
}

int
setenv (const char *name, const char *value, int replace)
{
  if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
    {
      __set_errno (EINVAL);
      return -1;
    }

  return __add_to_environ (name, value, NULL, replace);
}

/* The 'clearenv' was planned to be added to POSIX.1 but probably
   never made it.  Nevertheless the POSIX.9 standard (POSIX bindings
   for Fortran 77) requires this function.  */
int
clearenv (void)
{
  LOCK;

  if (__environ == last_environ && __environ != NULL)
    {
      /* We allocated this environment so we can free it.  */
      free (__environ);
      last_environ = NULL;
    }

  /* Clear the environment pointer removes the whole environment.  */
  __environ = NULL;

  UNLOCK;

  return 0;
}

#ifdef _LIBC
static void
free_mem (void)
{
  /* Remove all traces.  */
  clearenv ();

  /* Now remove the search tree.  */
  __tdestroy (known_values, free);
  known_values = NULL;
}
text_set_element (__libc_subfreeres, free_mem);


# undef setenv
# undef clearenv
weak_alias (__setenv, setenv)
weak_alias (__clearenv, clearenv)
#endif

#endif /* _LIBC || !HAVE_SETENV */

/* The rest of this file is called into use when replacing an existing
   but buggy setenv.  Known bugs include failure to diagnose invalid
   name, and consuming a leading '=' from value.  */
#if HAVE_SETENV

# undef setenv
# if !HAVE_DECL_SETENV
extern int setenv (const char *, const char *, int);
# endif
# define STREQ(a, b) (strcmp (a, b) == 0)

int
rpl_setenv (const char *name, const char *value, int replace)
{
  int result;
  if (!name || !*name || strchr (name, '='))
    {
      errno = EINVAL;
      return -1;
    }
  /* Call the real setenv even if replace is 0, in case implementation
     has underlying data to update, such as when environ changes.  */
  result = setenv (name, value, replace);
  if (result == 0 && replace && *value == '=')
    {
      char *tmp = getenv (name);
      if (!STREQ (tmp, value))
        {
          int saved_errno;
          size_t len = strlen (value);
          tmp = malloca (len + 2);
          if (tmp == NULL)
            {
              errno = ENOMEM;
              return -1;
            }
          /* Since leading '=' is eaten, double it up.  */
          *tmp = '=';
          memcpy (tmp + 1, value, len + 1);
          result = setenv (name, tmp, replace);
          saved_errno = errno;
          freea (tmp);
          errno = saved_errno;
        }
    }
  return result;
}

#endif /* HAVE_SETENV */