262 lines
9.3 KiB
C++
262 lines
9.3 KiB
C++
/*
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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 "ext4_utils/ext4_crypt.h"
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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 <string.h>
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#include <sys/syscall.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 <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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#define XATTR_NAME_ENCRYPTION_POLICY "encryption.policy"
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#define EXT4_KEYREF_DELIMITER ((char)'.')
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// ext4enc:TODO Include structure from somewhere sensible
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// MUST be in sync with ext4_crypto.c in kernel
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#define EXT4_KEY_DESCRIPTOR_SIZE 8
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#define EXT4_KEY_DESCRIPTOR_SIZE_HEX 17
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struct ext4_encryption_policy {
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uint8_t version;
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uint8_t contents_encryption_mode;
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uint8_t filenames_encryption_mode;
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uint8_t flags;
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uint8_t master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
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} __attribute__((__packed__));
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#define EXT4_ENCRYPTION_MODE_AES_256_XTS 1
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#define EXT4_ENCRYPTION_MODE_AES_256_CTS 4
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#define EXT4_ENCRYPTION_MODE_AES_256_HEH 126
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#define EXT4_ENCRYPTION_MODE_PRIVATE 127
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#define EXT4_POLICY_FLAGS_PAD_4 0x00
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#define EXT4_POLICY_FLAGS_PAD_8 0x01
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#define EXT4_POLICY_FLAGS_PAD_16 0x02
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#define EXT4_POLICY_FLAGS_PAD_32 0x03
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#define EXT4_POLICY_FLAGS_PAD_MASK 0x03
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#define EXT4_POLICY_FLAGS_VALID 0x03
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// ext4enc:TODO Get value from somewhere sensible
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#define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
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#define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
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#define HEX_LOOKUP "0123456789abcdef"
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bool e4crypt_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 policy_to_hex(const char* policy, char* hex) {
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for (size_t i = 0, j = 0; i < EXT4_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[EXT4_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 e4crypt_get_policy_flags(int filenames_encryption_mode) {
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// With HEH, pad filenames with zeroes to the next 16-byte boundary. This
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// is not required, but it's more secure (helps hide the length of
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// filenames), makes the inputs evenly divisible into blocks which is more
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// efficient for encryption and decryption, and we had the opportunity to
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// make a breaking change when introducing a new mode anyway.
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if (filenames_encryption_mode == EXT4_ENCRYPTION_MODE_AES_256_HEH) {
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return EXT4_POLICY_FLAGS_PAD_16;
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}
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// Default flags (4-byte padding) for CTS
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return EXT4_POLICY_FLAGS_PAD_4;
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}
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static bool e4crypt_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 != EXT4_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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ext4_encryption_policy eep;
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eep.version = 0;
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eep.contents_encryption_mode = contents_encryption_mode;
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eep.filenames_encryption_mode = filenames_encryption_mode;
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eep.flags = e4crypt_get_policy_flags(filenames_encryption_mode);
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memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE);
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if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) {
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PLOG(ERROR) << "Failed to set encryption policy for " << directory;
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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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char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
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policy_to_hex(policy, policy_hex);
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LOG(INFO) << "Policy for " << directory << " set to " << policy_hex;
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return true;
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}
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static bool e4crypt_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 != EXT4_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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ext4_encryption_policy eep;
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memset(&eep, 0, sizeof(ext4_encryption_policy));
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if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) {
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PLOG(ERROR) << "Failed to get encryption policy for " << directory;
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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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if ((eep.version != 0)
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|| (eep.contents_encryption_mode != contents_encryption_mode)
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|| (eep.filenames_encryption_mode != filenames_encryption_mode)
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|| (eep.flags !=
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e4crypt_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, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE);
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return true;
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}
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static bool e4crypt_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 != EXT4_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[EXT4_KEY_DESCRIPTOR_SIZE];
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if (!e4crypt_policy_get(directory, existing_policy, EXT4_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[EXT4_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, EXT4_KEY_DESCRIPTOR_SIZE) != 0) {
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char policy_hex[EXT4_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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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 e4crypt_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 = EXT4_ENCRYPTION_MODE_AES_256_XTS;
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} else if (!strcmp(contents_encryption_mode, "ice")) {
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contents_mode = EXT4_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 = EXT4_ENCRYPTION_MODE_AES_256_CTS;
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} else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
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filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_HEH;
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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 (!e4crypt_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 (!e4crypt_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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