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      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 
     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 
     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 
     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 
    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 
    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 
    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 
    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