/*
* 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 <array>
#include <asm/ioctl.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/fs.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <cutils/properties.h>
#include <logwrap/logwrap.h>
#include <utils/misc.h>
#define FS_KEY_DESCRIPTOR_SIZE_HEX (2 * FS_KEY_DESCRIPTOR_SIZE + 1)
/* modes not supported by upstream kernel, so not in <linux/fs.h> */
#define FS_ENCRYPTION_MODE_AES_256_HEH 126
#define FS_ENCRYPTION_MODE_PRIVATE 127
/* new definition, not yet in Bionic's <linux/fs.h> */
#ifndef FS_ENCRYPTION_MODE_ADIANTUM
#define FS_ENCRYPTION_MODE_ADIANTUM 9
#endif
/* new definition, not yet in Bionic's <linux/fs.h> */
#ifndef FS_POLICY_FLAG_DIRECT_KEY
#define FS_POLICY_FLAG_DIRECT_KEY 0x4
#endif
#define HEX_LOOKUP "0123456789abcdef"
bool fscrypt_is_native() {
char value[PROPERTY_VALUE_MAX];
property_get("ro.crypto.type", value, "none");
return !strcmp(value, "file");
}
static void log_ls(const char* dirname) {
std::array<const char*, 3> argv = {"ls", "-laZ", dirname};
int status = 0;
auto res =
android_fork_execvp(argv.size(), const_cast<char**>(argv.data()), &status, false, true);
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;
}
}
static void policy_to_hex(const char* policy, char* hex) {
for (size_t i = 0, j = 0; i < FS_KEY_DESCRIPTOR_SIZE; i++) {
hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4];
hex[j++] = HEX_LOOKUP[policy[i] & 0x0F];
}
hex[FS_KEY_DESCRIPTOR_SIZE_HEX - 1] = '\0';
}
static bool is_dir_empty(const char *dirname, bool *is_empty)
{
int n = 0;
auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(dirname), closedir);
if (!dirp) {
PLOG(ERROR) << "Unable to read directory: " << dirname;
return false;
}
for (;;) {
errno = 0;
auto entry = readdir(dirp.get());
if (!entry) {
if (errno) {
PLOG(ERROR) << "Unable to read directory: " << dirname;
return false;
}
break;
}
if (strcmp(entry->d_name, "lost+found") != 0) { // Skip lost+found
++n;
if (n > 2) {
*is_empty = false;
return true;
}
}
}
*is_empty = true;
return true;
}
static uint8_t fscrypt_get_policy_flags(int filenames_encryption_mode) {
if (filenames_encryption_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
// Use legacy padding with our original filenames encryption mode.
return FS_POLICY_FLAGS_PAD_4;
} else if (filenames_encryption_mode == FS_ENCRYPTION_MODE_ADIANTUM) {
// 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
return (FS_POLICY_FLAGS_PAD_16 | FS_POLICY_FLAG_DIRECT_KEY);
}
// With a new mode we can use the better padding flag without breaking existing devices: pad
// filenames with zeroes to the next 16-byte boundary. This is more secure (helps hide the
// length of filenames) and makes the inputs evenly divisible into blocks which is more
// efficient for encryption and decryption.
return FS_POLICY_FLAGS_PAD_16;
}
static bool fscrypt_policy_set(const char *directory, const char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != FS_KEY_DESCRIPTOR_SIZE) {
LOG(ERROR) << "Policy wrong length: " << policy_length;
return false;
}
char policy_hex[FS_KEY_DESCRIPTOR_SIZE_HEX];
policy_to_hex(policy, policy_hex);
int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
if (fd == -1) {
PLOG(ERROR) << "Failed to open directory " << directory;
return false;
}
fscrypt_policy fp;
fp.version = 0;
fp.contents_encryption_mode = contents_encryption_mode;
fp.filenames_encryption_mode = filenames_encryption_mode;
fp.flags = fscrypt_get_policy_flags(filenames_encryption_mode);
memcpy(fp.master_key_descriptor, policy, FS_KEY_DESCRIPTOR_SIZE);
if (ioctl(fd, FS_IOC_SET_ENCRYPTION_POLICY, &fp)) {
PLOG(ERROR) << "Failed to set encryption policy for " << directory << " to " << policy_hex
<< " modes " << contents_encryption_mode << "/" << filenames_encryption_mode;
close(fd);
return false;
}
close(fd);
LOG(INFO) << "Policy for " << directory << " set to " << policy_hex
<< " modes " << contents_encryption_mode << "/" << filenames_encryption_mode;
return true;
}
static bool fscrypt_policy_get(const char *directory, char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != FS_KEY_DESCRIPTOR_SIZE) {
LOG(ERROR) << "Policy wrong length: " << policy_length;
return false;
}
int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
if (fd == -1) {
PLOG(ERROR) << "Failed to open directory " << directory;
return false;
}
fscrypt_policy fp;
memset(&fp, 0, sizeof(fscrypt_policy));
if (ioctl(fd, FS_IOC_GET_ENCRYPTION_POLICY, &fp) != 0) {
PLOG(ERROR) << "Failed to get encryption policy for " << directory;
close(fd);
log_ls(directory);
return false;
}
close(fd);
if ((fp.version != 0)
|| (fp.contents_encryption_mode != contents_encryption_mode)
|| (fp.filenames_encryption_mode != filenames_encryption_mode)
|| (fp.flags !=
fscrypt_get_policy_flags(filenames_encryption_mode))) {
LOG(ERROR) << "Failed to find matching encryption policy for " << directory;
return false;
}
memcpy(policy, fp.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
return true;
}
static bool fscrypt_policy_check(const char *directory, const char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != FS_KEY_DESCRIPTOR_SIZE) {
LOG(ERROR) << "Policy wrong length: " << policy_length;
return false;
}
char existing_policy[FS_KEY_DESCRIPTOR_SIZE];
if (!fscrypt_policy_get(directory, existing_policy, FS_KEY_DESCRIPTOR_SIZE,
contents_encryption_mode,
filenames_encryption_mode)) return false;
char existing_policy_hex[FS_KEY_DESCRIPTOR_SIZE_HEX];
policy_to_hex(existing_policy, existing_policy_hex);
if (memcmp(policy, existing_policy, FS_KEY_DESCRIPTOR_SIZE) != 0) {
char policy_hex[FS_KEY_DESCRIPTOR_SIZE_HEX];
policy_to_hex(policy, policy_hex);
LOG(ERROR) << "Found policy " << existing_policy_hex << " at " << directory
<< " which doesn't match expected value " << policy_hex;
log_ls(directory);
return false;
}
LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory
<< " which matches expected value";
return true;
}
int fscrypt_policy_ensure(const char *directory, const char *policy,
size_t policy_length,
const char *contents_encryption_mode,
const char *filenames_encryption_mode) {
int contents_mode = 0;
int filenames_mode = 0;
if (!strcmp(contents_encryption_mode, "software") ||
!strcmp(contents_encryption_mode, "aes-256-xts")) {
contents_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
} else if (!strcmp(contents_encryption_mode, "adiantum")) {
contents_mode = FS_ENCRYPTION_MODE_ADIANTUM;
} else if (!strcmp(contents_encryption_mode, "ice")) {
contents_mode = FS_ENCRYPTION_MODE_PRIVATE;
} else {
LOG(ERROR) << "Invalid file contents encryption mode: "
<< contents_encryption_mode;
return -1;
}
if (!strcmp(filenames_encryption_mode, "aes-256-cts")) {
filenames_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
} else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
filenames_mode = FS_ENCRYPTION_MODE_AES_256_HEH;
} else if (!strcmp(filenames_encryption_mode, "adiantum")) {
filenames_mode = FS_ENCRYPTION_MODE_ADIANTUM;
} else {
LOG(ERROR) << "Invalid file names encryption mode: "
<< filenames_encryption_mode;
return -1;
}
bool is_empty;
if (!is_dir_empty(directory, &is_empty)) return -1;
if (is_empty) {
if (!fscrypt_policy_set(directory, policy, policy_length,
contents_mode, filenames_mode)) return -1;
} else {
if (!fscrypt_policy_check(directory, policy, policy_length,
contents_mode, filenames_mode)) return -1;
}
return 0;
}