a85bcc2e99
This is to make getenv() work correctly. Bug: http://b/20567629 Change-Id: I148627e1efea1649fb0822c95876811652fb4082
192 lines
5.3 KiB
C++
192 lines
5.3 KiB
C++
/*
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* Copyright (C) 2010 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "linker_environ.h"
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#include <linux/auxvec.h>
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#include <stddef.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include "private/KernelArgumentBlock.h"
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static bool _AT_SECURE_value = true;
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bool get_AT_SECURE() {
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return _AT_SECURE_value;
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}
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static void __init_AT_SECURE(KernelArgumentBlock& args) {
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// Check auxv for AT_SECURE first to see if program is setuid, setgid,
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// has file caps, or caused a SELinux/AppArmor domain transition.
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bool kernel_supplied_AT_SECURE;
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_AT_SECURE_value = args.getauxval(AT_SECURE, &kernel_supplied_AT_SECURE);
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// We don't support ancient kernels.
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if (!kernel_supplied_AT_SECURE) {
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const char* msg = "FATAL: kernel did not supply AT_SECURE\n";
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write(2, msg, strlen(msg));
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exit(EXIT_FAILURE);
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}
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}
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// Check if the environment variable definition at 'envstr'
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// starts with '<name>=', and if so return the address of the
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// first character after the equal sign. Otherwise return null.
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static const char* env_match(const char* envstr, const char* name) {
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size_t i = 0;
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while (envstr[i] == name[i] && name[i] != '\0') {
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++i;
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}
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if (name[i] == '\0' && envstr[i] == '=') {
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return envstr + i + 1;
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}
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return nullptr;
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}
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static bool __is_valid_environment_variable(const char* name) {
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// According to its sources, the kernel uses 32*PAGE_SIZE by default
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// as the maximum size for an env. variable definition.
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const int MAX_ENV_LEN = 32*4096;
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if (name == nullptr) {
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return false;
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}
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// Parse the string, looking for the first '=' there, and its size.
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int pos = 0;
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int first_equal_pos = -1;
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while (pos < MAX_ENV_LEN) {
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if (name[pos] == '\0') {
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break;
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}
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if (name[pos] == '=' && first_equal_pos < 0) {
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first_equal_pos = pos;
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}
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pos++;
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}
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// Check that it's smaller than MAX_ENV_LEN (to detect non-zero terminated strings).
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if (pos >= MAX_ENV_LEN) {
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return false;
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}
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// Check that it contains at least one equal sign that is not the first character
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if (first_equal_pos < 1) {
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return false;
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}
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return true;
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}
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static bool __is_unsafe_environment_variable(const char* name) {
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// None of these should be allowed in setuid programs.
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static const char* const UNSAFE_VARIABLE_NAMES[] = {
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"GCONV_PATH",
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"GETCONF_DIR",
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"HOSTALIASES",
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"JE_MALLOC_CONF",
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"LD_AOUT_LIBRARY_PATH",
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"LD_AOUT_PRELOAD",
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"LD_AUDIT",
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"LD_DEBUG",
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"LD_DEBUG_OUTPUT",
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"LD_DYNAMIC_WEAK",
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"LD_LIBRARY_PATH",
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"LD_ORIGIN_PATH",
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"LD_PRELOAD",
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"LD_PROFILE",
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"LD_SHOW_AUXV",
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"LD_USE_LOAD_BIAS",
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"LOCALDOMAIN",
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"LOCPATH",
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"MALLOC_CHECK_",
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"MALLOC_CONF",
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"MALLOC_TRACE",
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"NIS_PATH",
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"NLSPATH",
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"RESOLV_HOST_CONF",
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"RES_OPTIONS",
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"TMPDIR",
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"TZDIR",
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nullptr
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};
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for (size_t i = 0; UNSAFE_VARIABLE_NAMES[i] != nullptr; ++i) {
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if (env_match(name, UNSAFE_VARIABLE_NAMES[i]) != nullptr) {
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return true;
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}
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}
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return false;
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}
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static void __sanitize_environment_variables() {
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char** src = environ;
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char** dst = environ;
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for (; src[0] != nullptr; ++src) {
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if (!__is_valid_environment_variable(src[0])) {
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continue;
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}
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// Remove various unsafe environment variables if we're loading a setuid program.
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if (get_AT_SECURE() && __is_unsafe_environment_variable(src[0])) {
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continue;
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}
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dst[0] = src[0];
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++dst;
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}
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dst[0] = nullptr;
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}
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void linker_env_init(KernelArgumentBlock& args) {
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// Store environment pointer - can't be null.
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environ = args.envp;
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__init_AT_SECURE(args);
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__sanitize_environment_variables();
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}
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const char* linker_env_get(const char* name) {
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if (name == nullptr || name[0] == '\0') {
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return nullptr;
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}
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for (char** p = environ; p[0] != nullptr; ++p) {
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const char* val = env_match(p[0], name);
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if (val != nullptr) {
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if (val[0] == '\0') {
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return nullptr; // Return null for empty strings.
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}
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return val;
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}
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}
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return nullptr;
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}
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