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_utils/ext4_crypt.h"
18
19 #include <array>
20
21 #include <asm/ioctl.h>
22 #include <dirent.h>
23 #include <errno.h>
24 #include <fcntl.h>
25 #include <string.h>
26 #include <sys/syscall.h>
27 #include <sys/stat.h>
28 #include <sys/types.h>
29 #include <unistd.h>
30
31 #include <android-base/file.h>
32 #include <android-base/logging.h>
33 #include <cutils/properties.h>
34 #include <logwrap/logwrap.h>
35 #include <utils/misc.h>
36
37 #define XATTR_NAME_ENCRYPTION_POLICY "encryption.policy"
38 #define EXT4_KEYREF_DELIMITER ((char)'.')
39
40 // ext4enc:TODO Include structure from somewhere sensible
41 // MUST be in sync with ext4_crypto.c in kernel
42 #define EXT4_KEY_DESCRIPTOR_SIZE 8
43 #define EXT4_KEY_DESCRIPTOR_SIZE_HEX 17
44
45 struct ext4_encryption_policy {
46 uint8_t version;
47 uint8_t contents_encryption_mode;
48 uint8_t filenames_encryption_mode;
49 uint8_t flags;
50 uint8_t master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
51 } __attribute__((__packed__));
52
53 #define EXT4_ENCRYPTION_MODE_AES_256_XTS 1
54 #define EXT4_ENCRYPTION_MODE_AES_256_CTS 4
55 #define EXT4_ENCRYPTION_MODE_SPECK128_256_XTS 7
56 #define EXT4_ENCRYPTION_MODE_SPECK128_256_CTS 8
57 #define EXT4_ENCRYPTION_MODE_AES_256_HEH 126
58 #define EXT4_ENCRYPTION_MODE_PRIVATE 127
59
60 #define EXT4_POLICY_FLAGS_PAD_4 0x00
61 #define EXT4_POLICY_FLAGS_PAD_8 0x01
62 #define EXT4_POLICY_FLAGS_PAD_16 0x02
63 #define EXT4_POLICY_FLAGS_PAD_32 0x03
64 #define EXT4_POLICY_FLAGS_PAD_MASK 0x03
65 #define EXT4_POLICY_FLAGS_VALID 0x03
66
67 // ext4enc:TODO Get value from somewhere sensible
68 #define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
69 #define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
70
71 #define HEX_LOOKUP "0123456789abcdef"
72
e4crypt_is_native()73 bool e4crypt_is_native() {
74 char value[PROPERTY_VALUE_MAX];
75 property_get("ro.crypto.type", value, "none");
76 return !strcmp(value, "file");
77 }
78
log_ls(const char * dirname)79 static void log_ls(const char* dirname) {
80 std::array<const char*, 3> argv = {"ls", "-laZ", dirname};
81 int status = 0;
82 auto res =
83 android_fork_execvp(argv.size(), const_cast<char**>(argv.data()), &status, false, true);
84 if (res != 0) {
85 PLOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2] << "failed";
86 return;
87 }
88 if (!WIFEXITED(status)) {
89 LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
90 << " did not exit normally, status: " << status;
91 return;
92 }
93 if (WEXITSTATUS(status) != 0) {
94 LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
95 << " returned failure: " << WEXITSTATUS(status);
96 return;
97 }
98 }
99
policy_to_hex(const char * policy,char * hex)100 static void policy_to_hex(const char* policy, char* hex) {
101 for (size_t i = 0, j = 0; i < EXT4_KEY_DESCRIPTOR_SIZE; i++) {
102 hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4];
103 hex[j++] = HEX_LOOKUP[policy[i] & 0x0F];
104 }
105 hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX - 1] = '\0';
106 }
107
is_dir_empty(const char * dirname,bool * is_empty)108 static bool is_dir_empty(const char *dirname, bool *is_empty)
109 {
110 int n = 0;
111 auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(dirname), closedir);
112 if (!dirp) {
113 PLOG(ERROR) << "Unable to read directory: " << dirname;
114 return false;
115 }
116 for (;;) {
117 errno = 0;
118 auto entry = readdir(dirp.get());
119 if (!entry) {
120 if (errno) {
121 PLOG(ERROR) << "Unable to read directory: " << dirname;
122 return false;
123 }
124 break;
125 }
126 if (strcmp(entry->d_name, "lost+found") != 0) { // Skip lost+found
127 ++n;
128 if (n > 2) {
129 *is_empty = false;
130 return true;
131 }
132 }
133 }
134 *is_empty = true;
135 return true;
136 }
137
e4crypt_get_policy_flags(int filenames_encryption_mode)138 static uint8_t e4crypt_get_policy_flags(int filenames_encryption_mode) {
139 if (filenames_encryption_mode == EXT4_ENCRYPTION_MODE_AES_256_CTS) {
140 // Use legacy padding with our original filenames encryption mode.
141 return EXT4_POLICY_FLAGS_PAD_4;
142 }
143 // With a new mode we can use the better padding flag without breaking existing devices: pad
144 // filenames with zeroes to the next 16-byte boundary. This is more secure (helps hide the
145 // length of filenames) and makes the inputs evenly divisible into blocks which is more
146 // efficient for encryption and decryption.
147 return EXT4_POLICY_FLAGS_PAD_16;
148 }
149
e4crypt_policy_set(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)150 static bool e4crypt_policy_set(const char *directory, const char *policy,
151 size_t policy_length,
152 int contents_encryption_mode,
153 int filenames_encryption_mode) {
154 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
155 LOG(ERROR) << "Policy wrong length: " << policy_length;
156 return false;
157 }
158 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
159 policy_to_hex(policy, policy_hex);
160
161 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
162 if (fd == -1) {
163 PLOG(ERROR) << "Failed to open directory " << directory;
164 return false;
165 }
166
167 ext4_encryption_policy eep;
168 eep.version = 0;
169 eep.contents_encryption_mode = contents_encryption_mode;
170 eep.filenames_encryption_mode = filenames_encryption_mode;
171 eep.flags = e4crypt_get_policy_flags(filenames_encryption_mode);
172 memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE);
173 if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) {
174 PLOG(ERROR) << "Failed to set encryption policy for " << directory << " to " << policy_hex
175 << " modes " << contents_encryption_mode << "/" << filenames_encryption_mode;
176 close(fd);
177 return false;
178 }
179 close(fd);
180
181 LOG(INFO) << "Policy for " << directory << " set to " << policy_hex
182 << " modes " << contents_encryption_mode << "/" << filenames_encryption_mode;
183 return true;
184 }
185
e4crypt_policy_get(const char * directory,char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)186 static bool e4crypt_policy_get(const char *directory, char *policy,
187 size_t policy_length,
188 int contents_encryption_mode,
189 int filenames_encryption_mode) {
190 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
191 LOG(ERROR) << "Policy wrong length: " << policy_length;
192 return false;
193 }
194
195 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
196 if (fd == -1) {
197 PLOG(ERROR) << "Failed to open directory " << directory;
198 return false;
199 }
200
201 ext4_encryption_policy eep;
202 memset(&eep, 0, sizeof(ext4_encryption_policy));
203 if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) {
204 PLOG(ERROR) << "Failed to get encryption policy for " << directory;
205 close(fd);
206 log_ls(directory);
207 return false;
208 }
209 close(fd);
210
211 if ((eep.version != 0)
212 || (eep.contents_encryption_mode != contents_encryption_mode)
213 || (eep.filenames_encryption_mode != filenames_encryption_mode)
214 || (eep.flags !=
215 e4crypt_get_policy_flags(filenames_encryption_mode))) {
216 LOG(ERROR) << "Failed to find matching encryption policy for " << directory;
217 return false;
218 }
219 memcpy(policy, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE);
220
221 return true;
222 }
223
e4crypt_policy_check(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)224 static bool e4crypt_policy_check(const char *directory, const char *policy,
225 size_t policy_length,
226 int contents_encryption_mode,
227 int filenames_encryption_mode) {
228 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
229 LOG(ERROR) << "Policy wrong length: " << policy_length;
230 return false;
231 }
232 char existing_policy[EXT4_KEY_DESCRIPTOR_SIZE];
233 if (!e4crypt_policy_get(directory, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE,
234 contents_encryption_mode,
235 filenames_encryption_mode)) return false;
236 char existing_policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
237
238 policy_to_hex(existing_policy, existing_policy_hex);
239
240 if (memcmp(policy, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE) != 0) {
241 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
242 policy_to_hex(policy, policy_hex);
243 LOG(ERROR) << "Found policy " << existing_policy_hex << " at " << directory
244 << " which doesn't match expected value " << policy_hex;
245 log_ls(directory);
246 return false;
247 }
248 LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory
249 << " which matches expected value";
250 return true;
251 }
252
e4crypt_policy_ensure(const char * directory,const char * policy,size_t policy_length,const char * contents_encryption_mode,const char * filenames_encryption_mode)253 int e4crypt_policy_ensure(const char *directory, const char *policy,
254 size_t policy_length,
255 const char *contents_encryption_mode,
256 const char *filenames_encryption_mode) {
257 int contents_mode = 0;
258 int filenames_mode = 0;
259
260 if (!strcmp(contents_encryption_mode, "software") ||
261 !strcmp(contents_encryption_mode, "aes-256-xts")) {
262 contents_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
263 } else if (!strcmp(contents_encryption_mode, "speck128/256-xts")) {
264 contents_mode = EXT4_ENCRYPTION_MODE_SPECK128_256_XTS;
265 } else if (!strcmp(contents_encryption_mode, "ice")) {
266 contents_mode = EXT4_ENCRYPTION_MODE_PRIVATE;
267 } else {
268 LOG(ERROR) << "Invalid file contents encryption mode: "
269 << contents_encryption_mode;
270 return -1;
271 }
272
273 if (!strcmp(filenames_encryption_mode, "aes-256-cts")) {
274 filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_CTS;
275 } else if (!strcmp(filenames_encryption_mode, "speck128/256-cts")) {
276 filenames_mode = EXT4_ENCRYPTION_MODE_SPECK128_256_CTS;
277 } else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
278 filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_HEH;
279 } else {
280 LOG(ERROR) << "Invalid file names encryption mode: "
281 << filenames_encryption_mode;
282 return -1;
283 }
284
285 bool is_empty;
286 if (!is_dir_empty(directory, &is_empty)) return -1;
287 if (is_empty) {
288 if (!e4crypt_policy_set(directory, policy, policy_length,
289 contents_mode, filenames_mode)) return -1;
290 } else {
291 if (!e4crypt_policy_check(directory, policy, policy_length,
292 contents_mode, filenames_mode)) return -1;
293 }
294 return 0;
295 }
296