/* $NetBSD: _env.c,v 1.13 2022/03/12 17:31:39 christos Exp $ */
/*-
* Copyright (c) 2010 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Matthias Scheler.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: _env.c,v 1.13 2022/03/12 17:31:39 christos Exp $");
#endif /* LIBC_SCCS and not lint */
#include "namespace.h"
#include <sys/rbtree.h>
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include "csu-common.h"
#include "env.h"
#include "local.h"
/*
* Red-Black tree node for tracking memory used by environment variables.
* The tree is sorted by the address of the nodes themselves.
*/
typedef struct {
rb_node_t rb_node;
size_t length;
uint8_t marker;
char data[];
} env_node_t;
/* Compare functions for above tree. */
static signed int env_tree_compare_nodes(void *, const void *, const void *);
static signed int env_tree_compare_key(void *, const void *, const void *);
/* Operations for above tree. */
static const rb_tree_ops_t env_tree_ops = {
.rbto_compare_nodes = env_tree_compare_nodes,
.rbto_compare_key = env_tree_compare_key,
.rbto_node_offset = offsetof(env_node_t, rb_node),
.rbto_context = NULL
};
/* The single instance of above tree. */
static rb_tree_t env_tree;
/* The allocated environment. */
static char **allocated_environ;
static size_t allocated_environ_size;
#define ENV_ARRAY_SIZE_MIN 16
/* The lock protecting access to the environment. */
#ifdef _REENTRANT
static rwlock_t env_lock = RWLOCK_INITIALIZER;
#endif
/* Compatibility function. */
char *__findenv(const char *name, int *offsetp);
__warn_references(__findenv,
"warning: __findenv is an internal obsolete function.")
/* Our initialization function. */
void __libc_env_init(void);
/*ARGSUSED*/
static signed int
env_tree_compare_nodes(void *ctx, const void *node_a, const void *node_b)
{
uintptr_t addr_a, addr_b;
addr_a = (uintptr_t)node_a;
addr_b = (uintptr_t)node_b;
if (addr_a < addr_b)
return -1;
if (addr_a > addr_b)
return 1;
return 0;
}
static signed int
env_tree_compare_key(void *ctx, const void *node, const void *key)
{
return env_tree_compare_nodes(ctx, node,
(const uint8_t *)key - offsetof(env_node_t, data));
}
/*
* Determine the of the name in an environment string. Return 0 if the
* name is not valid.
*/
size_t
__envvarnamelen(const char *str, bool withequal)
{
size_t l_name;
if (str == NULL)
return 0;
l_name = strcspn(str, "=");
if (l_name == 0)
return 0;
if (withequal) {
if (str[l_name] != '=')
return 0;
} else {
if (str[l_name] == '=')
return 0;
}
return l_name;
}
/*
* Free memory occupied by environment variable if possible. This function
* must be called with the environment write locked.
*/
void
__freeenvvar(char *envvar)
{
env_node_t *node;
_DIAGASSERT(envvar != NULL);
node = rb_tree_find_node(&env_tree, envvar);
if (node != NULL) {
rb_tree_remove_node(&env_tree, node);
free(node);
}
}
/*
* Allocate memory for an environment variable. This function must be called
* with the environment write locked.
*/
char *
__allocenvvar(size_t length)
{
env_node_t *node;
node = malloc(sizeof(*node) + length);
if (node != NULL) {
node->length = length;
node->marker = 0;
rb_tree_insert_node(&env_tree, node);
return node->data;
} else {
return NULL;
}
}
/*
* Check whether an environment variable is writable. This function must be
* called with the environment write locked as the caller will probably
* overwrite the environment variable afterwards.
*/
bool
__canoverwriteenvvar(char *envvar, size_t length)
{
env_node_t *node;
_DIAGASSERT(envvar != NULL);
node = rb_tree_find_node(&env_tree, envvar);
return (node != NULL && length <= node->length);
}
/* Free all allocated environment variables that are no longer used. */
static void
__scrubenv(void)
{
static uint8_t marker = 0;
size_t num_entries;
env_node_t *node, *next;
while (++marker == 0);
/* Mark all nodes which are currently used. */
for (num_entries = 0; environ[num_entries] != NULL; num_entries++) {
node = rb_tree_find_node(&env_tree, environ[num_entries]);
if (node != NULL)
node->marker = marker;
}
/* Free all nodes which are currently not used. */
for (node = RB_TREE_MIN(&env_tree); node != NULL; node = next) {
next = rb_tree_iterate(&env_tree, node, RB_DIR_RIGHT);
if (node->marker != marker) {
rb_tree_remove_node(&env_tree, node);
free(node);
}
}
/* Deal with the environment array itself. */
if (environ == allocated_environ) {
/* Clear out spurious entries in the environment. */
(void)memset(&environ[num_entries + 1], 0,
(allocated_environ_size - num_entries - 1) *
sizeof(*environ));
} else {
/*
* The environment array was not allocated by "libc".
* Free our array if we allocated one.
*/
free(allocated_environ);
allocated_environ = NULL;
allocated_environ_size = 0;
}
}
/*
* Get a (new) slot in the environment. This function must be called with
* the environment write locked.
*/
ssize_t
__getenvslot(const char *name, size_t l_name, bool allocate)
{
size_t new_size, num_entries, required_size;
char **new_environ;
/* Search for an existing environment variable of the given name. */
num_entries = 0;
if (environ != NULL) {
while (environ[num_entries] != NULL) {
if (strncmp(environ[num_entries], name, l_name) == 0 &&
environ[num_entries][l_name] == '=') {
/* We found a match. */
return num_entries;
}
num_entries ++;
}
}
/* No match found, return if we don't want to allocate a new slot. */
if (!allocate)
return -1;
/* Does the environ need scrubbing? */
if (environ != allocated_environ && allocated_environ != NULL)
__scrubenv();
/* Create a new slot in the environment. */
required_size = num_entries + 1;
if (environ == allocated_environ &&
required_size < allocated_environ_size) {
/* Does the environment need scrubbing? */
if (required_size < allocated_environ_size &&
allocated_environ[required_size] != NULL) {
__scrubenv();
}
/* Return a free slot. */
return num_entries;
}
/* Determine size of a new environment array. */
new_size = ENV_ARRAY_SIZE_MIN;
while (new_size <= required_size)
new_size <<= 1;
/* Allocate a new environment array. */
if (environ == allocated_environ) {
new_environ = environ;
errno = reallocarr(&new_environ,
new_size, sizeof(*new_environ));
if (errno)
return -1;
} else {
free(allocated_environ);
allocated_environ = NULL;
allocated_environ_size = 0;
new_environ = NULL;
errno = reallocarr(&new_environ,
new_size, sizeof(*new_environ));
if (errno)
return -1;
(void)memcpy(new_environ, environ,
num_entries * sizeof(*new_environ));
}
/* Clear remaining entries. */
(void)memset(&new_environ[num_entries], 0,
(new_size - num_entries) * sizeof(*new_environ));
/* Use the new environment array. */
environ = allocated_environ = new_environ;
allocated_environ_size = new_size;
/* Return a free slot. */
return num_entries;
}
/* Find a string in the environment. */
char *
__findenvvar(const char *name, size_t l_name)
{
ssize_t offset;
offset = __getenvslot(name, l_name, false);
return (offset != -1) ? environ[offset] + l_name + 1 : NULL;
}
/* Compatibility interface, do *not* call this function. */
char *
__findenv(const char *name, int *offsetp)
{
size_t l_name;
ssize_t offset;
l_name = __envvarnamelen(name, false);
if (l_name == 0)
return NULL;
offset = __getenvslot(name, l_name, false);
if (offset < 0 || offset > INT_MAX)
return NULL;
*offsetp = (int)offset;
return environ[offset] + l_name + 1;
}
#ifdef _REENTRANT
/* Lock the environment for read. */
bool
__readlockenv(void)
{
int error;
error = rwlock_rdlock(&env_lock);
if (error == 0)
return true;
errno = error;
return false;
}
/* Lock the environment for write. */
bool
__writelockenv(void)
{
int error;
error = rwlock_wrlock(&env_lock);
if (error == 0)
return true;
errno = error;
return false;
}
/* Unlock the environment for write. */
bool
__unlockenv(void)
{
int error;
error = rwlock_unlock(&env_lock);
if (error == 0)
return true;
errno = error;
return false;
}
#endif
/* Initialize environment memory RB tree. */
void __section(".text.startup")
__libc_env_init(void)
{
rb_tree_init(&env_tree, &env_tree_ops);
}