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/file.h>
31 #include <android-base/logging.h>
32 #include <cutils/properties.h>
33
34 #define XATTR_NAME_ENCRYPTION_POLICY "encryption.policy"
35 #define EXT4_KEYREF_DELIMITER ((char)'.')
36
37 // ext4enc:TODO Include structure from somewhere sensible
38 // MUST be in sync with ext4_crypto.c in kernel
39 #define EXT4_KEY_DESCRIPTOR_SIZE 8
40 #define EXT4_KEY_DESCRIPTOR_SIZE_HEX 17
41
42 struct ext4_encryption_policy {
43 char version;
44 char contents_encryption_mode;
45 char filenames_encryption_mode;
46 char flags;
47 char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
48 } __attribute__((__packed__));
49
50 #define EXT4_ENCRYPTION_MODE_AES_256_XTS 1
51 #define EXT4_ENCRYPTION_MODE_AES_256_CTS 4
52 #define EXT4_ENCRYPTION_MODE_PRIVATE 127
53
54 // ext4enc:TODO Get value from somewhere sensible
55 #define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
56 #define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
57
58 #define HEX_LOOKUP "0123456789abcdef"
59
e4crypt_is_native()60 bool e4crypt_is_native() {
61 char value[PROPERTY_VALUE_MAX];
62 property_get("ro.crypto.type", value, "none");
63 return !strcmp(value, "file");
64 }
65
policy_to_hex(const char * policy,char * hex)66 static void policy_to_hex(const char* policy, char* hex) {
67 for (size_t i = 0, j = 0; i < EXT4_KEY_DESCRIPTOR_SIZE; i++) {
68 hex[j++] = HEX_LOOKUP[(policy[i] & 0xF0) >> 4];
69 hex[j++] = HEX_LOOKUP[policy[i] & 0x0F];
70 }
71 hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX - 1] = '\0';
72 }
73
is_dir_empty(const char * dirname,bool * is_empty)74 static bool is_dir_empty(const char *dirname, bool *is_empty)
75 {
76 int n = 0;
77 auto dirp = std::unique_ptr<DIR, int (*)(DIR*)>(opendir(dirname), closedir);
78 if (!dirp) {
79 PLOG(ERROR) << "Unable to read directory: " << dirname;
80 return false;
81 }
82 for (;;) {
83 errno = 0;
84 auto entry = readdir(dirp.get());
85 if (!entry) {
86 if (errno) {
87 PLOG(ERROR) << "Unable to read directory: " << dirname;
88 return false;
89 }
90 break;
91 }
92 if (strcmp(entry->d_name, "lost+found") != 0) { // Skip lost+found
93 ++n;
94 if (n > 2) {
95 *is_empty = false;
96 return true;
97 }
98 }
99 }
100 *is_empty = true;
101 return true;
102 }
103
e4crypt_policy_set(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode)104 static bool e4crypt_policy_set(const char *directory, const char *policy,
105 size_t policy_length, int contents_encryption_mode) {
106 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
107 LOG(ERROR) << "Policy wrong length: " << policy_length;
108 return false;
109 }
110 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
111 if (fd == -1) {
112 PLOG(ERROR) << "Failed to open directory " << directory;
113 return false;
114 }
115
116 ext4_encryption_policy eep;
117 eep.version = 0;
118 eep.contents_encryption_mode = contents_encryption_mode;
119 eep.filenames_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_CTS;
120 eep.flags = 0;
121 memcpy(eep.master_key_descriptor, policy, EXT4_KEY_DESCRIPTOR_SIZE);
122 if (ioctl(fd, EXT4_IOC_SET_ENCRYPTION_POLICY, &eep)) {
123 PLOG(ERROR) << "Failed to set encryption policy for " << directory;
124 close(fd);
125 return false;
126 }
127 close(fd);
128
129 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
130 policy_to_hex(policy, policy_hex);
131 LOG(INFO) << "Policy for " << directory << " set to " << policy_hex;
132 return true;
133 }
134
e4crypt_policy_get(const char * directory,char * policy,size_t policy_length,int contents_encryption_mode)135 static bool e4crypt_policy_get(const char *directory, char *policy,
136 size_t policy_length, int contents_encryption_mode) {
137 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
138 LOG(ERROR) << "Policy wrong length: " << policy_length;
139 return false;
140 }
141
142 int fd = open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
143 if (fd == -1) {
144 PLOG(ERROR) << "Failed to open directory " << directory;
145 return false;
146 }
147
148 ext4_encryption_policy eep;
149 memset(&eep, 0, sizeof(ext4_encryption_policy));
150 if (ioctl(fd, EXT4_IOC_GET_ENCRYPTION_POLICY, &eep) != 0) {
151 PLOG(ERROR) << "Failed to get encryption policy for " << directory;
152 close(fd);
153 return -1;
154 }
155 close(fd);
156
157 if ((eep.version != 0)
158 || (eep.contents_encryption_mode != contents_encryption_mode)
159 || (eep.filenames_encryption_mode != EXT4_ENCRYPTION_MODE_AES_256_CTS)
160 || (eep.flags != 0)) {
161 LOG(ERROR) << "Failed to find matching encryption policy for " << directory;
162 return false;
163 }
164 memcpy(policy, eep.master_key_descriptor, EXT4_KEY_DESCRIPTOR_SIZE);
165
166 return true;
167 }
168
e4crypt_policy_check(const char * directory,const char * policy,size_t policy_length,int contents_encryption_mode)169 static bool e4crypt_policy_check(const char *directory, const char *policy,
170 size_t policy_length, int contents_encryption_mode) {
171 if (policy_length != EXT4_KEY_DESCRIPTOR_SIZE) {
172 LOG(ERROR) << "Policy wrong length: " << policy_length;
173 return false;
174 }
175 char existing_policy[EXT4_KEY_DESCRIPTOR_SIZE];
176 if (!e4crypt_policy_get(directory, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE,
177 contents_encryption_mode)) return false;
178 char existing_policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
179
180 policy_to_hex(existing_policy, existing_policy_hex);
181
182 if (memcmp(policy, existing_policy, EXT4_KEY_DESCRIPTOR_SIZE) != 0) {
183 char policy_hex[EXT4_KEY_DESCRIPTOR_SIZE_HEX];
184 policy_to_hex(policy, policy_hex);
185 LOG(ERROR) << "Found policy " << existing_policy_hex << " at " << directory
186 << " which doesn't match expected value " << policy_hex;
187 return false;
188 }
189 LOG(INFO) << "Found policy " << existing_policy_hex << " at " << directory
190 << " which matches expected value";
191 return true;
192 }
193
e4crypt_policy_ensure(const char * directory,const char * policy,size_t policy_length,const char * contents_encryption_mode)194 int e4crypt_policy_ensure(const char *directory, const char *policy,
195 size_t policy_length, const char* contents_encryption_mode) {
196 int mode = 0;
197 if (!strcmp(contents_encryption_mode, "software")) {
198 mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
199 } else if (!strcmp(contents_encryption_mode, "ice")) {
200 mode = EXT4_ENCRYPTION_MODE_PRIVATE;
201 } else {
202 LOG(ERROR) << "Invalid encryption mode";
203 return -1;
204 }
205
206 bool is_empty;
207 if (!is_dir_empty(directory, &is_empty)) return -1;
208 if (is_empty) {
209 if (!e4crypt_policy_set(directory, policy, policy_length,
210 mode)) return -1;
211 } else {
212 if (!e4crypt_policy_check(directory, policy, policy_length,
213 mode)) return -1;
214 }
215 return 0;
216 }
217