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aosp12/system/extras/libfscrypt/fscrypt.cpp

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