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367 lines
13 KiB
367 lines
13 KiB
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "fscrypt/fscrypt.h"
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#include <android-base/file.h>
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#include <android-base/logging.h>
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#include <android-base/properties.h>
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#include <android-base/strings.h>
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#include <android-base/unique_fd.h>
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#include <asm/ioctl.h>
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#include <cutils/properties.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/fscrypt.h>
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#include <logwrap/logwrap.h>
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#include <string.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <utils/misc.h>
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#include <array>
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#include <string>
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#include <vector>
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using namespace std::string_literals;
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/* modes not supported by upstream kernel, so not in <linux/fscrypt.h> */
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#define FSCRYPT_MODE_AES_256_HEH 126
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#define FSCRYPT_MODE_PRIVATE 127
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#define HEX_LOOKUP "0123456789abcdef"
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struct ModeLookupEntry {
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std::string name;
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int id;
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};
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static const auto contents_modes = std::vector<ModeLookupEntry>{
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{"aes-256-xts"s, FSCRYPT_MODE_AES_256_XTS},
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{"software"s, FSCRYPT_MODE_AES_256_XTS},
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{"adiantum"s, FSCRYPT_MODE_ADIANTUM},
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{"ice"s, FSCRYPT_MODE_PRIVATE},
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};
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static const auto filenames_modes = std::vector<ModeLookupEntry>{
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{"aes-256-cts"s, FSCRYPT_MODE_AES_256_CTS},
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{"aes-256-heh"s, FSCRYPT_MODE_AES_256_HEH},
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{"adiantum"s, FSCRYPT_MODE_ADIANTUM},
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};
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static bool LookupModeByName(const std::vector<struct ModeLookupEntry>& modes,
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const std::string& name, int* result) {
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for (const auto& e : modes) {
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if (e.name == name) {
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*result = e.id;
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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 bool LookupModeById(const std::vector<struct ModeLookupEntry>& modes, int id,
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std::string* result) {
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for (const auto& e : modes) {
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if (e.id == id) {
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*result = e.name;
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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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bool fscrypt_is_native() {
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char value[PROPERTY_VALUE_MAX];
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property_get("ro.crypto.type", value, "none");
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return !strcmp(value, "file");
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}
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namespace android {
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namespace fscrypt {
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static void log_ls(const char* dirname) {
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std::array<const char*, 3> argv = {"ls", "-laZ", dirname};
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int status = 0;
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auto res =
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logwrap_fork_execvp(argv.size(), argv.data(), &status, false, LOG_ALOG, false, nullptr);
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if (res != 0) {
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PLOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2] << "failed";
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return;
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}
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if (!WIFEXITED(status)) {
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LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
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<< " did not exit normally, status: " << status;
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return;
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}
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if (WEXITSTATUS(status) != 0) {
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LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
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<< " returned failure: " << WEXITSTATUS(status);
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return;
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}
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}
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void BytesToHex(const std::string& bytes, std::string* hex) {
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hex->clear();
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for (char c : bytes) {
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*hex += HEX_LOOKUP[(c & 0xF0) >> 4];
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*hex += HEX_LOOKUP[c & 0x0F];
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}
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}
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static bool fscrypt_is_encrypted(int fd) {
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fscrypt_policy_v1 policy;
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// success => encrypted with v1 policy
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// EINVAL => encrypted with v2 policy
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// ENODATA => not encrypted
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return ioctl(fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) == 0 || errno == EINVAL;
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}
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unsigned int GetFirstApiLevel() {
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return android::base::GetUintProperty<unsigned int>("ro.product.first_api_level", 0);
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}
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bool OptionsToString(const EncryptionOptions& options, std::string* options_string) {
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return OptionsToStringForApiLevel(GetFirstApiLevel(), options, options_string);
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}
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bool OptionsToStringForApiLevel(unsigned int first_api_level, const EncryptionOptions& options,
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std::string* options_string) {
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std::string contents_mode, filenames_mode;
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if (!LookupModeById(contents_modes, options.contents_mode, &contents_mode)) {
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return false;
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}
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if (!LookupModeById(filenames_modes, options.filenames_mode, &filenames_mode)) {
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return false;
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}
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*options_string = contents_mode + ":" + filenames_mode + ":v" + std::to_string(options.version);
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if ((options.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)) {
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*options_string += "+inlinecrypt_optimized";
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}
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if ((options.flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) {
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*options_string += "+emmc_optimized";
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}
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if (options.use_hw_wrapped_key) {
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*options_string += "+wrappedkey_v0";
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}
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EncryptionOptions options_check;
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if (!ParseOptionsForApiLevel(first_api_level, *options_string, &options_check)) {
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LOG(ERROR) << "Internal error serializing options as string: " << *options_string;
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return false;
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}
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if (options != options_check) {
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LOG(ERROR) << "Internal error serializing options as string, round trip failed: "
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<< *options_string;
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return false;
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}
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return true;
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}
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bool ParseOptions(const std::string& options_string, EncryptionOptions* options) {
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return ParseOptionsForApiLevel(GetFirstApiLevel(), options_string, options);
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}
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bool ParseOptionsForApiLevel(unsigned int first_api_level, const std::string& options_string,
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EncryptionOptions* options) {
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auto parts = android::base::Split(options_string, ":");
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if (parts.size() > 3) {
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LOG(ERROR) << "Invalid encryption options: " << options;
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return false;
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}
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options->contents_mode = FSCRYPT_MODE_AES_256_XTS;
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if (parts.size() > 0 && !parts[0].empty()) {
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if (!LookupModeByName(contents_modes, parts[0], &options->contents_mode)) {
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LOG(ERROR) << "Invalid file contents encryption mode: " << parts[0];
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return false;
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}
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}
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if (options->contents_mode == FSCRYPT_MODE_ADIANTUM) {
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options->filenames_mode = FSCRYPT_MODE_ADIANTUM;
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} else {
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options->filenames_mode = FSCRYPT_MODE_AES_256_CTS;
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}
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if (parts.size() > 1 && !parts[1].empty()) {
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if (!LookupModeByName(filenames_modes, parts[1], &options->filenames_mode)) {
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LOG(ERROR) << "Invalid file names encryption mode: " << parts[1];
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return false;
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}
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}
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// Default to v2 after Q
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options->version = first_api_level > __ANDROID_API_Q__ ? 2 : 1;
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options->flags = 0;
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options->use_hw_wrapped_key = false;
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if (parts.size() > 2 && !parts[2].empty()) {
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auto flags = android::base::Split(parts[2], "+");
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for (const auto& flag : flags) {
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if (flag == "v1") {
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options->version = 1;
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} else if (flag == "v2") {
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options->version = 2;
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} else if (flag == "inlinecrypt_optimized") {
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options->flags |= FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64;
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} else if (flag == "emmc_optimized") {
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options->flags |= FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32;
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} else if (flag == "wrappedkey_v0") {
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options->use_hw_wrapped_key = true;
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} else {
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LOG(ERROR) << "Unknown flag: " << flag;
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return false;
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}
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}
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}
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// In the original setting of v1 policies and AES-256-CTS we used 4-byte
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// padding of filenames, so retain that on old first_api_levels.
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//
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// For everything else, use 16-byte padding. This is more secure (it helps
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// hide the length of filenames), and it makes the inputs evenly divisible
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// into cipher blocks which is more efficient for encryption and decryption.
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if (first_api_level <= __ANDROID_API_Q__ && options->version == 1 &&
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options->filenames_mode == FSCRYPT_MODE_AES_256_CTS) {
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options->flags |= FSCRYPT_POLICY_FLAGS_PAD_4;
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} else {
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options->flags |= FSCRYPT_POLICY_FLAGS_PAD_16;
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}
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// Use DIRECT_KEY for Adiantum, since it's much more efficient but just as
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// secure since Android doesn't reuse the same master key for multiple
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// encryption modes.
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if (options->contents_mode == FSCRYPT_MODE_ADIANTUM) {
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if (options->filenames_mode != FSCRYPT_MODE_ADIANTUM) {
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LOG(ERROR) << "Adiantum must be both contents and filenames mode or neither, invalid "
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"options: "
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<< options_string;
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return false;
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}
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options->flags |= FSCRYPT_POLICY_FLAG_DIRECT_KEY;
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} else if (options->filenames_mode == FSCRYPT_MODE_ADIANTUM) {
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LOG(ERROR)
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<< "Adiantum must be both contents and filenames mode or neither, invalid options: "
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<< options_string;
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return false;
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}
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// IV generation methods are mutually exclusive
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int iv_methods = 0;
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iv_methods += !!(options->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64);
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iv_methods += !!(options->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32);
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iv_methods += !!(options->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
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if (iv_methods > 1) {
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LOG(ERROR) << "At most one IV generation method can be set, invalid options: "
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<< options_string;
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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 std::string PolicyDebugString(const EncryptionPolicy& policy) {
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std::stringstream ss;
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std::string ref_hex;
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BytesToHex(policy.key_raw_ref, &ref_hex);
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ss << ref_hex;
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ss << " v" << policy.options.version;
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ss << " modes " << policy.options.contents_mode << "/" << policy.options.filenames_mode;
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ss << std::hex << " flags 0x" << policy.options.flags;
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return ss.str();
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}
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bool EnsurePolicy(const EncryptionPolicy& policy, const std::string& directory) {
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union {
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fscrypt_policy_v1 v1;
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fscrypt_policy_v2 v2;
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} kern_policy;
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memset(&kern_policy, 0, sizeof(kern_policy));
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switch (policy.options.version) {
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case 1:
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if (policy.key_raw_ref.size() != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
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LOG(ERROR) << "Invalid key descriptor length for v1 policy: "
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<< policy.key_raw_ref.size();
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return false;
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}
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// Careful: FSCRYPT_POLICY_V1 is actually 0 in the API, so make sure
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// to use it here instead of a literal 1.
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kern_policy.v1.version = FSCRYPT_POLICY_V1;
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kern_policy.v1.contents_encryption_mode = policy.options.contents_mode;
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kern_policy.v1.filenames_encryption_mode = policy.options.filenames_mode;
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kern_policy.v1.flags = policy.options.flags;
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policy.key_raw_ref.copy(reinterpret_cast<char*>(kern_policy.v1.master_key_descriptor),
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FSCRYPT_KEY_DESCRIPTOR_SIZE);
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break;
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case 2:
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if (policy.key_raw_ref.size() != FSCRYPT_KEY_IDENTIFIER_SIZE) {
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LOG(ERROR) << "Invalid key identifier length for v2 policy: "
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<< policy.key_raw_ref.size();
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return false;
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}
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kern_policy.v2.version = FSCRYPT_POLICY_V2;
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kern_policy.v2.contents_encryption_mode = policy.options.contents_mode;
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kern_policy.v2.filenames_encryption_mode = policy.options.filenames_mode;
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kern_policy.v2.flags = policy.options.flags;
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policy.key_raw_ref.copy(reinterpret_cast<char*>(kern_policy.v2.master_key_identifier),
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FSCRYPT_KEY_IDENTIFIER_SIZE);
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break;
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default:
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LOG(ERROR) << "Invalid encryption policy version: " << policy.options.version;
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return false;
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}
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android::base::unique_fd fd(open(directory.c_str(), O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open directory " << directory;
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return false;
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}
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bool already_encrypted = fscrypt_is_encrypted(fd);
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// FS_IOC_SET_ENCRYPTION_POLICY will set the policy if the directory is
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// unencrypted; otherwise it will verify that the existing policy matches.
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// Setting the policy will fail if the directory is already nonempty.
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if (ioctl(fd, FS_IOC_SET_ENCRYPTION_POLICY, &kern_policy) != 0) {
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std::string reason;
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switch (errno) {
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case EEXIST:
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reason = "The directory already has a different encryption policy.";
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break;
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default:
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reason = strerror(errno);
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break;
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}
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LOG(ERROR) << "Failed to set encryption policy of " << directory << " to "
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<< PolicyDebugString(policy) << ": " << reason;
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if (errno == ENOTEMPTY) {
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log_ls(directory.c_str());
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}
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return false;
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}
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if (already_encrypted) {
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LOG(INFO) << "Verified that " << directory << " has the encryption policy "
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<< PolicyDebugString(policy);
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} else {
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LOG(INFO) << "Encryption policy of " << directory << " set to "
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<< PolicyDebugString(policy);
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}
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return true;
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}
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} // namespace fscrypt
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} // namespace android
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