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 <asm/ioctl.h>
20 #include <dirent.h>
21 #include <errno.h>
22 #include <fcntl.h>
23 #include <string.h>
24 #include <sys/syscall.h>
25 #include <sys/stat.h>
26 #include <sys/types.h>
27 #include <unistd.h>
28
29 #include <android-base/file.h>
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 uint8_t version;
43 uint8_t contents_encryption_mode;
44 uint8_t filenames_encryption_mode;
45 uint8_t flags;
46 uint8_t 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 #define EXT4_ENCRYPTION_MODE_AES_256_HEH 126
52 #define EXT4_ENCRYPTION_MODE_PRIVATE 127
53
54 #define EXT4_POLICY_FLAGS_PAD_4 0x00
55 #define EXT4_POLICY_FLAGS_PAD_8 0x01
56 #define EXT4_POLICY_FLAGS_PAD_16 0x02
57 #define EXT4_POLICY_FLAGS_PAD_32 0x03
58 #define EXT4_POLICY_FLAGS_PAD_MASK 0x03
59 #define EXT4_POLICY_FLAGS_VALID 0x03
60
61 // ext4enc:TODO Get value from somewhere sensible
62 #define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
63 #define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
64
65 #define HEX_LOOKUP "0123456789abcdef"
66
e4crypt_is_native()67 bool e4crypt_is_native() {
68 char value[PROPERTY_VALUE_MAX];
69 property_get("ro.crypto.type", value, "none");
70 return !strcmp(value, "file");
71 }
72
policy_to_hex(const char * policy,char * hex)73 static void policy_to_hex(const char* policy, char* hex) {
74 for (size_t i = 0, j = 0; i < EXT4_KEY_DESCRIPTOR_SIZE; i++) {
75 hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4];
76 hex[j++] = HEX_LOOKUP[policy[i] & 0x0F];
77 }
78 hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX - 1] = '\0';
79 }
80
is_dir_empty(const char * dirname,bool * is_empty)81 static bool is_dir_empty(const char *dirname, bool *is_empty)
82 {
83 int n = 0;
84 auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(dirname), closedir);
85 if (!dirp) {
86 PLOG(ERROR) << "Unable to read directory: " << dirname;
87 return false;
88 }
89 for (;;) {
90 errno = 0;
91 auto entry = readdir(dirp.get());
92 if (!entry) {
93 if (errno) {
94 PLOG(ERROR) << "Unable to read directory: " << dirname;
95 return false;
96 }
97 break;
98 }
99 if (strcmp(entry->d_name, "lost+found") != 0) { // Skip lost+found
100 ++n;
101 if (n > 2) {
102 *is_empty = false;
103 return true;
104 }
105 }
106 }
107 *is_empty = true;
108 return true;
109 }
110
e4crypt_get_policy_flags(int filenames_encryption_mode)111 static uint8_t e4crypt_get_policy_flags(int filenames_encryption_mode) {
112
113 // With HEH, pad filenames with zeroes to the next 16-byte boundary. This
114 // is not required, but it's more secure (helps hide the length of
115 // filenames), makes the inputs evenly divisible into blocks which is more
116 // efficient for encryption and decryption, and we had the opportunity to
117 // make a breaking change when introducing a new mode anyway.
118 if (filenames_encryption_mode == EXT4_ENCRYPTION_MODE_AES_256_HEH) {
119 return EXT4_POLICY_FLAGS_PAD_16;
120 }
121
122 // Default flags (4-byte padding) for CTS
123 return EXT4_POLICY_FLAGS_PAD_4;
124 }
125
e4crypt_policy_set(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)126 static bool e4crypt_policy_set(const char *directory, const char *policy,
127 size_t policy_length,
128 int contents_encryption_mode,
129 int filenames_encryption_mode) {
130 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
131 LOG(ERROR) << "Policy wrong length: " << policy_length;
132 return false;
133 }
134 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
135 if (fd == -1) {
136 PLOG(ERROR) << "Failed to open directory " << directory;
137 return false;
138 }
139
140 ext4_encryption_policy eep;
141 eep.version = 0;
142 eep.contents_encryption_mode = contents_encryption_mode;
143 eep.filenames_encryption_mode = filenames_encryption_mode;
144 eep.flags = e4crypt_get_policy_flags(filenames_encryption_mode);
145 memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE);
146 if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) {
147 PLOG(ERROR) << "Failed to set encryption policy for " << directory;
148 close(fd);
149 return false;
150 }
151 close(fd);
152
153 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
154 policy_to_hex(policy, policy_hex);
155 LOG(INFO) << "Policy for " << directory << " set to " << policy_hex;
156 return true;
157 }
158
e4crypt_policy_get(const char * directory,char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)159 static bool e4crypt_policy_get(const char *directory, char *policy,
160 size_t policy_length,
161 int contents_encryption_mode,
162 int filenames_encryption_mode) {
163 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
164 LOG(ERROR) << "Policy wrong length: " << policy_length;
165 return false;
166 }
167
168 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
169 if (fd == -1) {
170 PLOG(ERROR) << "Failed to open directory " << directory;
171 return false;
172 }
173
174 ext4_encryption_policy eep;
175 memset(&eep, 0, sizeof(ext4_encryption_policy));
176 if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) {
177 PLOG(ERROR) << "Failed to get encryption policy for " << directory;
178 close(fd);
179 return false;
180 }
181 close(fd);
182
183 if ((eep.version != 0)
184 || (eep.contents_encryption_mode != contents_encryption_mode)
185 || (eep.filenames_encryption_mode != filenames_encryption_mode)
186 || (eep.flags !=
187 e4crypt_get_policy_flags(filenames_encryption_mode))) {
188 LOG(ERROR) << "Failed to find matching encryption policy for " << directory;
189 return false;
190 }
191 memcpy(policy, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE);
192
193 return true;
194 }
195
e4crypt_policy_check(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode,int filenames_encryption_mode)196 static bool e4crypt_policy_check(const char *directory, const char *policy,
197 size_t policy_length,
198 int contents_encryption_mode,
199 int filenames_encryption_mode) {
200 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
201 LOG(ERROR) << "Policy wrong length: " << policy_length;
202 return false;
203 }
204 char existing_policy[EXT4_KEY_DESCRIPTOR_SIZE];
205 if (!e4crypt_policy_get(directory, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE,
206 contents_encryption_mode,
207 filenames_encryption_mode)) return false;
208 char existing_policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
209
210 policy_to_hex(existing_policy, existing_policy_hex);
211
212 if (memcmp(policy, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE) != 0) {
213 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
214 policy_to_hex(policy, policy_hex);
215 LOG(ERROR) << "Found policy " << existing_policy_hex << " at " << directory
216 << " which doesn't match expected value " << policy_hex;
217 return false;
218 }
219 LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory
220 << " which matches expected value";
221 return true;
222 }
223
e4crypt_policy_ensure(const char * directory,const char * policy,size_t policy_length,const char * contents_encryption_mode,const char * filenames_encryption_mode)224 int e4crypt_policy_ensure(const char *directory, const char *policy,
225 size_t policy_length,
226 const char *contents_encryption_mode,
227 const char *filenames_encryption_mode) {
228 int contents_mode = 0;
229 int filenames_mode = 0;
230
231 if (!strcmp(contents_encryption_mode, "software") ||
232 !strcmp(contents_encryption_mode, "aes-256-xts")) {
233 contents_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
234 } else if (!strcmp(contents_encryption_mode, "ice")) {
235 contents_mode = EXT4_ENCRYPTION_MODE_PRIVATE;
236 } else {
237 LOG(ERROR) << "Invalid file contents encryption mode: "
238 << contents_encryption_mode;
239 return -1;
240 }
241
242 if (!strcmp(filenames_encryption_mode, "aes-256-cts")) {
243 filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_CTS;
244 } else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
245 filenames_mode = EXT4_ENCRYPTION_MODE_AES_256_HEH;
246 } else {
247 LOG(ERROR) << "Invalid file names encryption mode: "
248 << filenames_encryption_mode;
249 return -1;
250 }
251
252 bool is_empty;
253 if (!is_dir_empty(directory, &is_empty)) return -1;
254 if (is_empty) {
255 if (!e4crypt_policy_set(directory, policy, policy_length,
256 contents_mode, filenames_mode)) return -1;
257 } else {
258 if (!e4crypt_policy_check(directory, policy, policy_length,
259 contents_mode, filenames_mode)) return -1;
260 }
261 return 0;
262 }
263