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
42struct 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
60bool e4crypt_is_native() {
61    char value[PROPERTY_VALUE_MAX];
62    property_get("ro.crypto.type", value, "none");
63    return !strcmp(value, "file");
64}
65
66static 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
74static 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
104static 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
135static 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
169static 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
194int 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