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PL286/system/extras/ext4_utils/ext4_crypt.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 "ext4_utils/ext4_crypt.h"
#include <asm/ioctl.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <cutils/properties.h>
#define XATTR_NAME_ENCRYPTION_POLICY "encryption.policy"
#define EXT4_KEYREF_DELIMITER ((char)'.')
// ext4enc:TODO Include structure from somewhere sensible
// MUST be in sync with ext4_crypto.c in kernel
#define EXT4_KEY_DESCRIPTOR_SIZE 8
#define EXT4_KEY_DESCRIPTOR_SIZE_HEX 17
struct ext4_encryption_policy {
uint8_t version;
uint8_t contents_encryption_mode;
uint8_t filenames_encryption_mode;
uint8_t flags;
uint8_t master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
} __attribute__((__packed__));
#define EXT4_ENCRYPTION_MODE_AES_256_XTS 1
#define EXT4_ENCRYPTION_MODE_AES_256_CTS 4
#define EXT4_ENCRYPTION_MODE_AES_256_HEH 126
#define EXT4_ENCRYPTION_MODE_PRIVATE 127
#define EXT4_POLICY_FLAGS_PAD_4 0x00
#define EXT4_POLICY_FLAGS_PAD_8 0x01
#define EXT4_POLICY_FLAGS_PAD_16 0x02
#define EXT4_POLICY_FLAGS_PAD_32 0x03
#define EXT4_POLICY_FLAGS_PAD_MASK 0x03
#define EXT4_POLICY_FLAGS_VALID 0x03
// ext4enc:TODO Get value from somewhere sensible
#define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
#define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
#define HEX_LOOKUP "0123456789abcdef"
bool e4crypt_is_native() {
char value[PROPERTY_VALUE_MAX];
property_get("ro.crypto.type", value, "none");
return !strcmp(value, "file");
}
static void policy_to_hex(const char* policy, char* hex) {
for (size_t i = 0, j = 0; i < EXT4_KEY_DESCRIPTOR_SIZE; i++) {
hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4];
hex[j++] = HEX_LOOKUP[policy[i] & 0x0F];
}
hex[EXT4_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 e4crypt_get_policy_flags(int filenames_encryption_mode) {
// With HEH, pad filenames with zeroes to the next 16-byte boundary. This
// is not required, but it's more secure (helps hide the length of
// filenames), makes the inputs evenly divisible into blocks which is more
// efficient for encryption and decryption, and we had the opportunity to
// make a breaking change when introducing a new mode anyway.
if (filenames_encryption_mode == EXT4_ENCRYPTION_MODE_AES_256_HEH) {
return EXT4_POLICY_FLAGS_PAD_16;
}
// Default flags (4-byte padding) for CTS
return EXT4_POLICY_FLAGS_PAD_4;
}
static bool e4crypt_policy_set(const char *directory, const char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != EXT4_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;
}
ext4_encryption_policy eep;
eep.version = 0;
eep.contents_encryption_mode = contents_encryption_mode;
eep.filenames_encryption_mode = filenames_encryption_mode;
eep.flags = e4crypt_get_policy_flags(filenames_encryption_mode);
memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE);
if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) {
PLOG(ERROR) << "Failed to set encryption policy for " << directory;
close(fd);
return false;
}
close(fd);
char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
policy_to_hex(policy, policy_hex);
LOG(INFO) << "Policy for " << directory << " set to " << policy_hex;
return true;
}
static bool e4crypt_policy_get(const char *directory, char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != EXT4_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;
}
ext4_encryption_policy eep;
memset(&eep, 0, sizeof(ext4_encryption_policy));
if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) {
PLOG(ERROR) << "Failed to get encryption policy for " << directory;
close(fd);
return false;
}
close(fd);
if ((eep.version != 0)
|| (eep.contents_encryption_mode != contents_encryption_mode)
|| (eep.filenames_encryption_mode != filenames_encryption_mode)
|| (eep.flags !=
e4crypt_get_policy_flags(filenames_encryption_mode))) {
LOG(ERROR) << "Failed to find matching encryption policy for " << directory;
return false;
}
memcpy(policy, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE);
return true;
}
static bool e4crypt_policy_check(const char *directory, const char *policy,
size_t policy_length,
int contents_encryption_mode,
int filenames_encryption_mode) {
if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
LOG(ERROR) << "Policy wrong length: " << policy_length;
return false;
}
char existing_policy[EXT4_KEY_DESCRIPTOR_SIZE];
if (!e4crypt_policy_get(directory, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE,
contents_encryption_mode,
filenames_encryption_mode)) return false;
char existing_policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
policy_to_hex(existing_policy, existing_policy_hex);
if (memcmp(policy, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE) != 0) {
char policy_hex[EXT4_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;
return false;
}
LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory
<< " which matches expected value";
return true;
}
int e4crypt_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 = EXT4_ENCRYPTION_MODE_AES_256_XTS;
} else if (!strcmp(contents_encryption_mode, "ice")) {
contents_mode = EXT4_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 = EXT4_ENCRYPTION_MODE_AES_256_CTS;
} else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_HEH;
} 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 (!e4crypt_policy_set(directory, policy, policy_length,
contents_mode, filenames_mode)) return -1;
} else {
if (!e4crypt_policy_check(directory, policy, policy_length,
contents_mode, filenames_mode)) return -1;
}
return 0;
}