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