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
41struct 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
58bool e4crypt_is_native() {
59    char value[PROPERTY_VALUE_MAX];
60    property_get("ro.crypto.type", value, "none");
61    return !strcmp(value, "file");
62}
63
64static 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
72static 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
102static 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
132static 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
165static 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
188int 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