1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "ext4_crypt.h" 18 19 #include <dirent.h> 20 #include <errno.h> 21 #include <string.h> 22 #include <unistd.h> 23 24 #include <fcntl.h> 25 #include <asm/ioctl.h> 26 #include <sys/syscall.h> 27 #include <sys/stat.h> 28 #include <sys/types.h> 29 30 #include <android-base/logging.h> 31 #include <cutils/properties.h> 32 33 #define XATTR_NAME_ENCRYPTION_POLICY "encryption.policy" 34 #define EXT4_KEYREF_DELIMITER ((char)'.') 35 36 // ext4enc:TODO Include structure from somewhere sensible 37 // MUST be in sync with ext4_crypto.c in kernel 38 #define EXT4_KEY_DESCRIPTOR_SIZE 8 39 #define EXT4_KEY_DESCRIPTOR_SIZE_HEX 17 40 41 struct ext4_encryption_policy { 42 char version; 43 char contents_encryption_mode; 44 char filenames_encryption_mode; 45 char flags; 46 char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE]; 47 } __attribute__((__packed__)); 48 49 #define EXT4_ENCRYPTION_MODE_AES_256_XTS 1 50 #define EXT4_ENCRYPTION_MODE_AES_256_CTS 4 51 52 // ext4enc:TODO Get value from somewhere sensible 53 #define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy) 54 #define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy) 55 56 #define HEX_LOOKUP "0123456789abcdef" 57 58 bool e4crypt_is_native() { 59 char value[PROPERTY_VALUE_MAX]; 60 property_get("ro.crypto.type", value, "none"); 61 return !strcmp(value, "file"); 62 } 63 64 static void policy_to_hex(const char* policy, char* hex) { 65 for (size_t i = 0, j = 0; i < EXT4_KEY_DESCRIPTOR_SIZE; i++) { 66 hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4]; 67 hex[j++] = HEX_LOOKUP[policy[i] & 0x0F]; 68 } 69 hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX - 1] = '\0'; 70 } 71 72 static bool is_dir_empty(const char *dirname, bool *is_empty) 73 { 74 int n = 0; 75 auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(dirname), closedir); 76 if (!dirp) { 77 PLOG(ERROR) << "Unable to read directory: " << dirname; 78 return false; 79 } 80 for (;;) { 81 errno = 0; 82 auto entry = readdir(dirp.get()); 83 if (!entry) { 84 if (errno) { 85 PLOG(ERROR) << "Unable to read directory: " << dirname; 86 return false; 87 } 88 break; 89 } 90 if (strcmp(entry->d_name, "lost+found") != 0) { // Skip lost+found 91 ++n; 92 if (n > 2) { 93 *is_empty = false; 94 return true; 95 } 96 } 97 } 98 *is_empty = true; 99 return true; 100 } 101 102 static bool e4crypt_policy_set(const char *directory, const char *policy, size_t policy_length) { 103 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) { 104 LOG(ERROR) << "Policy wrong length: " << policy_length; 105 return false; 106 } 107 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC); 108 if (fd == -1) { 109 PLOG(ERROR) << "Failed to open directory " << directory; 110 return false; 111 } 112 113 ext4_encryption_policy eep; 114 eep.version = 0; 115 eep.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS; 116 eep.filenames_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_CTS; 117 eep.flags = 0; 118 memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE); 119 if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) { 120 PLOG(ERROR) << "Failed to set encryption policy for " << directory; 121 close(fd); 122 return false; 123 } 124 close(fd); 125 126 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX]; 127 policy_to_hex(policy, policy_hex); 128 LOG(INFO) << "Policy for " << directory << " set to " << policy_hex; 129 return true; 130 } 131 132 static bool e4crypt_policy_get(const char *directory, char *policy, size_t policy_length) { 133 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) { 134 LOG(ERROR) << "Policy wrong length: " << policy_length; 135 return false; 136 } 137 138 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC); 139 if (fd == -1) { 140 PLOG(ERROR) << "Failed to open directory " << directory; 141 return false; 142 } 143 144 ext4_encryption_policy eep; 145 memset(&eep, 0, sizeof(ext4_encryption_policy)); 146 if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) { 147 PLOG(ERROR) << "Failed to get encryption policy for " << directory; 148 close(fd); 149 return -1; 150 } 151 close(fd); 152 153 if ((eep.version != 0) 154 || (eep.contents_encryption_mode != EXT4_ENCRYPTION_MODE_AES_256_XTS) 155 || (eep.filenames_encryption_mode != EXT4_ENCRYPTION_MODE_AES_256_CTS) 156 || (eep.flags != 0)) { 157 LOG(ERROR) << "Failed to find matching encryption policy for " << directory; 158 return false; 159 } 160 memcpy(policy, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE); 161 162 return true; 163 } 164 165 static bool e4crypt_policy_check(const char *directory, const char *policy, size_t policy_length) { 166 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) { 167 LOG(ERROR) << "Policy wrong length: " << policy_length; 168 return false; 169 } 170 char existing_policy[EXT4_KEY_DESCRIPTOR_SIZE]; 171 if (!e4crypt_policy_get(directory, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE)) return false; 172 char existing_policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX]; 173 174 policy_to_hex(existing_policy, existing_policy_hex); 175 176 if (memcmp(policy, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE) != 0) { 177 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX]; 178 policy_to_hex(policy, policy_hex); 179 LOG(ERROR) << "Found policy " << existing_policy_hex << " at " << directory 180 << " which doesn't match expected value " << policy_hex; 181 return false; 182 } 183 LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory 184 << " which matches expected value"; 185 return true; 186 } 187 188 int e4crypt_policy_ensure(const char *directory, const char *policy, size_t policy_length) { 189 bool is_empty; 190 if (!is_dir_empty(directory, &is_empty)) return -1; 191 if (is_empty) { 192 if (!e4crypt_policy_set(directory, policy, policy_length)) return -1; 193 } else { 194 if (!e4crypt_policy_check(directory, policy, policy_length)) return -1; 195 } 196 return 0; 197 } 198
