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/*
* Copyright (C) 2010 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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 COPYRIGHT HOLDERS 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
* COPYRIGHT OWNER 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 "linker_environ.h"
#include <linux/auxvec.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "private/KernelArgumentBlock.h"
static char** _envp;
static bool _AT_SECURE_value = true;
bool get_AT_SECURE() {
return _AT_SECURE_value;
}
static void __init_AT_SECURE(KernelArgumentBlock& args) {
// Check auxv for AT_SECURE first to see if program is setuid, setgid,
// has file caps, or caused a SELinux/AppArmor domain transition.
bool kernel_supplied_AT_SECURE;
_AT_SECURE_value = args.getauxval(AT_SECURE, &kernel_supplied_AT_SECURE);
// We don't support ancient kernels.
if (!kernel_supplied_AT_SECURE) {
const char* msg = "FATAL: kernel did not supply AT_SECURE\n";
write(2, msg, strlen(msg));
exit(EXIT_FAILURE);
}
}
// Check if the environment variable definition at 'envstr'
// starts with '<name>=', and if so return the address of the
// first character after the equal sign. Otherwise return null.
static const char* env_match(const char* envstr, const char* name) {
size_t i = 0;
while (envstr[i] == name[i] && name[i] != '\0') {
++i;
}
if (name[i] == '\0' && envstr[i] == '=') {
return envstr + i + 1;
}
return nullptr;
}
static bool __is_valid_environment_variable(const char* name) {
// According to its sources, the kernel uses 32*PAGE_SIZE by default
// as the maximum size for an env. variable definition.
const int MAX_ENV_LEN = 32*4096;
if (name == nullptr) {
return false;
}
// Parse the string, looking for the first '=' there, and its size.
int pos = 0;
int first_equal_pos = -1;
while (pos < MAX_ENV_LEN) {
if (name[pos] == '\0') {
break;
}
if (name[pos] == '=' && first_equal_pos < 0) {
first_equal_pos = pos;
}
pos++;
}
// Check that it's smaller than MAX_ENV_LEN (to detect non-zero terminated strings).
if (pos >= MAX_ENV_LEN) {
return false;
}
// Check that it contains at least one equal sign that is not the first character
if (first_equal_pos < 1) {
return false;
}
return true;
}
static bool __is_unsafe_environment_variable(const char* name) {
// None of these should be allowed in setuid programs.
static const char* const UNSAFE_VARIABLE_NAMES[] = {
"GCONV_PATH",
"GETCONF_DIR",
"HOSTALIASES",
"JE_MALLOC_CONF",
"LD_AOUT_LIBRARY_PATH",
"LD_AOUT_PRELOAD",
"LD_AUDIT",
"LD_DEBUG",
"LD_DEBUG_OUTPUT",
"LD_DYNAMIC_WEAK",
"LD_LIBRARY_PATH",
"LD_ORIGIN_PATH",
"LD_PRELOAD",
"LD_PROFILE",
"LD_SHOW_AUXV",
"LD_USE_LOAD_BIAS",
"LOCALDOMAIN",
"LOCPATH",
"MALLOC_CHECK_",
"MALLOC_CONF",
"MALLOC_TRACE",
"NIS_PATH",
"NLSPATH",
"RESOLV_HOST_CONF",
"RES_OPTIONS",
"TMPDIR",
"TZDIR",
nullptr
};
for (size_t i = 0; UNSAFE_VARIABLE_NAMES[i] != nullptr; ++i) {
if (env_match(name, UNSAFE_VARIABLE_NAMES[i]) != nullptr) {
return true;
}
}
return false;
}
static void __sanitize_environment_variables() {
char** src = _envp;
char** dst = _envp;
for (; src[0] != nullptr; ++src) {
if (!__is_valid_environment_variable(src[0])) {
continue;
}
// Remove various unsafe environment variables if we're loading a setuid program.
if (get_AT_SECURE() && __is_unsafe_environment_variable(src[0])) {
continue;
}
dst[0] = src[0];
++dst;
}
dst[0] = nullptr;
}
void linker_env_init(KernelArgumentBlock& args) {
// Store environment pointer - can't be null.
_envp = args.envp;
__init_AT_SECURE(args);
__sanitize_environment_variables();
}
const char* linker_env_get(const char* name) {
if (name == nullptr || name[0] == '\0') {
return nullptr;
}
for (char** p = _envp; p[0] != nullptr; ++p) {
const char* val = env_match(p[0], name);
if (val != nullptr) {
if (val[0] == '\0') {
return nullptr; // Return null for empty strings.
}
return val;
}
}
return nullptr;
}
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