glibc/stdlib/setenv.c

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

   The GNU C Library 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.

   The GNU C Library 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 the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

/* Pacify GCC; see the commentary about VALLEN below.  This is needed
   at least through GCC 4.9.2.  Pacify GCC for the entire file, as
   there seems to be no way to pacify GCC selectively, only for the
   place where it's needed.  Do not use DIAG_IGNORE_NEEDS_COMMENT
   here, as it's not defined yet.  */
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"

#include <errno.h>
#if !_LIBC
# if !defined errno && !defined HAVE_ERRNO_DECL
extern int errno;
# endif
# define __set_errno(ev) ((errno) = (ev))
#endif

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

#if !_LIBC
# define __environ	environ
# ifndef HAVE_ENVIRON_DECL
extern char **environ;
# endif
#endif

#if _LIBC
/* This lock protects against simultaneous modifications of `environ'.  */
# include <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 unsetenv __unsetenv
# 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__)
# define USE_TSEARCH	1
# include <search.h>

/* 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;

  /* Compute lengths before locking, so that the critical section is
     less of a performance bottleneck.  VALLEN is needed only if
     COMBINED is null (unfortunately GCC is not smart enough to deduce
     this; see the #pragma at the start of this file).  Testing
     COMBINED instead of VALUE causes setenv (..., NULL, ...)  to dump
     core now instead of corrupting memory later.  */
  const size_t namelen = strlen (name);
  size_t vallen;
  if (combined == NULL)
    vallen = strlen (value) + 1;

  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 || __builtin_expect (*ep == NULL, 1))
    {
      char **new_environ;

      /* We allocated this space; we can extend it.  Avoid using the raw
	 reallocated pointer to avoid GCC -Wuse-after-free.  */
      uintptr_t ip_last_environ = (uintptr_t)last_environ;
      new_environ = (char **) realloc (last_environ,
				       (size + 2) * sizeof (char *));
      if (new_environ == NULL)
	{
	  UNLOCK;
	  return -1;
	}

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

      new_environ[size] = NULL;
      new_environ[size + 1] = NULL;
      ep = new_environ + size;

      last_environ = __environ = new_environ;
    }
  if (*ep == NULL || replace)
    {
      char *np;

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

	  np = KNOWN_VALUE (new_value);
	  if (__glibc_likely (np == NULL))
#endif
	    {
#ifdef USE_TSEARCH
	      if (__glibc_unlikely (! use_alloca))
		np = new_value;
	      else
#endif
		{
		  np = malloc (varlen);
		  if (__glibc_unlikely (np == NULL))
		    {
		      UNLOCK;
		      return -1;
		    }

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

int
unsetenv (const char *name)
{
  size_t len;
  char **ep;

  if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
    {
      __set_errno (EINVAL);
      return -1;
    }

  len = strlen (name);

  LOCK;

  ep = __environ;
  if (ep != NULL)
    while (*ep != NULL)
      {
	if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
	  {
	    /* Found it.  Remove this pointer by moving later ones back.  */
	    char **dp = ep;

	    do
		dp[0] = dp[1];
	    while (*dp++);
	    /* Continue the loop in case NAME appears again.  */
	  }
	else
	  ++ep;
      }

  UNLOCK;

  return 0;
}

/* 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
void
__libc_setenv_freemem (void)
{
  /* Remove all traces.  */
  clearenv ();

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

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