fs_mgr_verity.c revision 4cafe2ff89b49329e0e880900195d8e061bd3750 
1/*
2 * Copyright (C) 2013 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 <inttypes.h>
18#include <stdio.h>
19#include <stdlib.h>
20#include <string.h>
21#include <unistd.h>
22#include <fcntl.h>
23#include <ctype.h>
24#include <sys/mount.h>
25#include <sys/stat.h>
26#include <errno.h>
27#include <sys/types.h>
28#include <sys/wait.h>
29#include <libgen.h>
30#include <time.h>
31
32#include <private/android_filesystem_config.h>
33#include <cutils/properties.h>
34#include <logwrap/logwrap.h>
35
36#include "mincrypt/rsa.h"
37#include "mincrypt/sha.h"
38#include "mincrypt/sha256.h"
39
40#include "ext4_sb.h"
41
42#include "fs_mgr_priv.h"
43#include "fs_mgr_priv_verity.h"
44
45#define VERITY_METADATA_SIZE 32768
46#define VERITY_TABLE_RSA_KEY "/verity_key"
47
48extern struct fs_info info;
49
50static RSAPublicKey *load_key(char *path)
51{
52    FILE *f;
53    RSAPublicKey *key;
54
55    key = malloc(sizeof(RSAPublicKey));
56    if (!key) {
57        ERROR("Can't malloc key\n");
58        return NULL;
59    }
60
61    f = fopen(path, "r");
62    if (!f) {
63        ERROR("Can't open '%s'\n", path);
64        free(key);
65        return NULL;
66    }
67
68    if (!fread(key, sizeof(*key), 1, f)) {
69        ERROR("Could not read key!");
70        fclose(f);
71        free(key);
72        return NULL;
73    }
74
75    if (key->len != RSANUMWORDS) {
76        ERROR("Invalid key length %d\n", key->len);
77        fclose(f);
78        free(key);
79        return NULL;
80    }
81
82    fclose(f);
83    return key;
84}
85
86static int verify_table(char *signature, char *table, int table_length)
87{
88    RSAPublicKey *key;
89    uint8_t hash_buf[SHA_DIGEST_SIZE];
90    int retval = -1;
91
92    // Hash the table
93    SHA_hash((uint8_t*)table, table_length, hash_buf);
94
95    // Now get the public key from the keyfile
96    key = load_key(VERITY_TABLE_RSA_KEY);
97    if (!key) {
98        ERROR("Couldn't load verity keys");
99        goto out;
100    }
101
102    // verify the result
103    if (!RSA_verify(key,
104                    (uint8_t*) signature,
105                    RSANUMBYTES,
106                    (uint8_t*) hash_buf,
107                    SHA_DIGEST_SIZE)) {
108        ERROR("Couldn't verify table.");
109        goto out;
110    }
111
112    retval = 0;
113
114out:
115    free(key);
116    return retval;
117}
118
119static int get_target_device_size(char *blk_device, uint64_t *device_size)
120{
121    int data_device;
122    struct ext4_super_block sb;
123    struct fs_info info = {0};
124
125    data_device = TEMP_FAILURE_RETRY(open(blk_device, O_RDONLY | O_CLOEXEC));
126    if (data_device == -1) {
127        ERROR("Error opening block device (%s)", strerror(errno));
128        return -1;
129    }
130
131    if (TEMP_FAILURE_RETRY(lseek64(data_device, 1024, SEEK_SET)) < 0) {
132        ERROR("Error seeking to superblock");
133        TEMP_FAILURE_RETRY(close(data_device));
134        return -1;
135    }
136
137    if (TEMP_FAILURE_RETRY(read(data_device, &sb, sizeof(sb))) != sizeof(sb)) {
138        ERROR("Error reading superblock");
139        TEMP_FAILURE_RETRY(close(data_device));
140        return -1;
141    }
142
143    ext4_parse_sb(&sb, &info);
144    *device_size = info.len;
145
146    TEMP_FAILURE_RETRY(close(data_device));
147    return 0;
148}
149
150static int read_verity_metadata(char *block_device, char **signature, char **table)
151{
152    unsigned magic_number;
153    unsigned table_length;
154    uint64_t device_length;
155    int protocol_version;
156    int device;
157    int retval = FS_MGR_SETUP_VERITY_FAIL;
158    *signature = 0;
159    *table = 0;
160
161    device = TEMP_FAILURE_RETRY(open(block_device, O_RDONLY | O_CLOEXEC));
162    if (device == -1) {
163        ERROR("Could not open block device %s (%s).\n", block_device, strerror(errno));
164        goto out;
165    }
166
167    // find the start of the verity metadata
168    if (get_target_device_size(block_device, &device_length) < 0) {
169        ERROR("Could not get target device size.\n");
170        goto out;
171    }
172    if (TEMP_FAILURE_RETRY(lseek64(device, device_length, SEEK_SET)) < 0) {
173        ERROR("Could not seek to start of verity metadata block.\n");
174        goto out;
175    }
176
177    // check the magic number
178    if (TEMP_FAILURE_RETRY(read(device, &magic_number, sizeof(magic_number))) !=
179            sizeof(magic_number)) {
180        ERROR("Couldn't read magic number!\n");
181        goto out;
182    }
183
184#ifdef ALLOW_ADBD_DISABLE_VERITY
185    if (magic_number == VERITY_METADATA_MAGIC_DISABLE) {
186        retval = FS_MGR_SETUP_VERITY_DISABLED;
187        INFO("Attempt to cleanly disable verity - only works in USERDEBUG");
188        goto out;
189    }
190#endif
191
192    if (magic_number != VERITY_METADATA_MAGIC_NUMBER) {
193        ERROR("Couldn't find verity metadata at offset %"PRIu64"!\n",
194              device_length);
195        goto out;
196    }
197
198    // check the protocol version
199    if (TEMP_FAILURE_RETRY(read(device, &protocol_version,
200            sizeof(protocol_version))) != sizeof(protocol_version)) {
201        ERROR("Couldn't read verity metadata protocol version!\n");
202        goto out;
203    }
204    if (protocol_version != 0) {
205        ERROR("Got unknown verity metadata protocol version %d!\n", protocol_version);
206        goto out;
207    }
208
209    // get the signature
210    *signature = (char*) malloc(RSANUMBYTES);
211    if (!*signature) {
212        ERROR("Couldn't allocate memory for signature!\n");
213        goto out;
214    }
215    if (TEMP_FAILURE_RETRY(read(device, *signature, RSANUMBYTES)) != RSANUMBYTES) {
216        ERROR("Couldn't read signature from verity metadata!\n");
217        goto out;
218    }
219
220    // get the size of the table
221    if (TEMP_FAILURE_RETRY(read(device, &table_length, sizeof(table_length))) !=
222            sizeof(table_length)) {
223        ERROR("Couldn't get the size of the verity table from metadata!\n");
224        goto out;
225    }
226
227    // get the table + null terminator
228    *table = malloc(table_length + 1);
229    if (!*table) {
230        ERROR("Couldn't allocate memory for verity table!\n");
231        goto out;
232    }
233    if (TEMP_FAILURE_RETRY(read(device, *table, table_length)) !=
234            (ssize_t)table_length) {
235        ERROR("Couldn't read the verity table from metadata!\n");
236        goto out;
237    }
238
239    (*table)[table_length] = 0;
240    retval = FS_MGR_SETUP_VERITY_SUCCESS;
241
242out:
243    if (device != -1)
244        TEMP_FAILURE_RETRY(close(device));
245
246    if (retval != FS_MGR_SETUP_VERITY_SUCCESS) {
247        free(*table);
248        free(*signature);
249        *table = 0;
250        *signature = 0;
251    }
252
253    return retval;
254}
255
256static void verity_ioctl_init(struct dm_ioctl *io, char *name, unsigned flags)
257{
258    memset(io, 0, DM_BUF_SIZE);
259    io->data_size = DM_BUF_SIZE;
260    io->data_start = sizeof(struct dm_ioctl);
261    io->version[0] = 4;
262    io->version[1] = 0;
263    io->version[2] = 0;
264    io->flags = flags | DM_READONLY_FLAG;
265    if (name) {
266        strlcpy(io->name, name, sizeof(io->name));
267    }
268}
269
270static int create_verity_device(struct dm_ioctl *io, char *name, int fd)
271{
272    verity_ioctl_init(io, name, 1);
273    if (ioctl(fd, DM_DEV_CREATE, io)) {
274        ERROR("Error creating device mapping (%s)", strerror(errno));
275        return -1;
276    }
277    return 0;
278}
279
280static int get_verity_device_name(struct dm_ioctl *io, char *name, int fd, char **dev_name)
281{
282    verity_ioctl_init(io, name, 0);
283    if (ioctl(fd, DM_DEV_STATUS, io)) {
284        ERROR("Error fetching verity device number (%s)", strerror(errno));
285        return -1;
286    }
287    int dev_num = (io->dev & 0xff) | ((io->dev >> 12) & 0xfff00);
288    if (asprintf(dev_name, "/dev/block/dm-%u", dev_num) < 0) {
289        ERROR("Error getting verity block device name (%s)", strerror(errno));
290        return -1;
291    }
292    return 0;
293}
294
295static int load_verity_table(struct dm_ioctl *io, char *name, char *blockdev, int fd, char *table)
296{
297    char *verity_params;
298    char *buffer = (char*) io;
299    uint64_t device_size = 0;
300
301    if (get_target_device_size(blockdev, &device_size) < 0) {
302        return -1;
303    }
304
305    verity_ioctl_init(io, name, DM_STATUS_TABLE_FLAG);
306
307    struct dm_target_spec *tgt = (struct dm_target_spec *) &buffer[sizeof(struct dm_ioctl)];
308
309    // set tgt arguments here
310    io->target_count = 1;
311    tgt->status=0;
312    tgt->sector_start=0;
313    tgt->length=device_size/512;
314    strcpy(tgt->target_type, "verity");
315
316    // build the verity params here
317    verity_params = buffer + sizeof(struct dm_ioctl) + sizeof(struct dm_target_spec);
318    if (sprintf(verity_params, "%s", table) < 0) {
319        return -1;
320    }
321
322    // set next target boundary
323    verity_params += strlen(verity_params) + 1;
324    verity_params = (char*) (((unsigned long)verity_params + 7) & ~8);
325    tgt->next = verity_params - buffer;
326
327    // send the ioctl to load the verity table
328    if (ioctl(fd, DM_TABLE_LOAD, io)) {
329        ERROR("Error loading verity table (%s)", strerror(errno));
330        return -1;
331    }
332
333    return 0;
334}
335
336static int resume_verity_table(struct dm_ioctl *io, char *name, int fd)
337{
338    verity_ioctl_init(io, name, 0);
339    if (ioctl(fd, DM_DEV_SUSPEND, io)) {
340        ERROR("Error activating verity device (%s)", strerror(errno));
341        return -1;
342    }
343    return 0;
344}
345
346static int test_access(char *device) {
347    int tries = 25;
348    while (tries--) {
349        if (!access(device, F_OK) || errno != ENOENT) {
350            return 0;
351        }
352        usleep(40 * 1000);
353    }
354    return -1;
355}
356
357static int set_verified_property(char *name) {
358    int ret;
359    char *key;
360    ret = asprintf(&key, "partition.%s.verified", name);
361    if (ret < 0) {
362        ERROR("Error formatting verified property");
363        return ret;
364    }
365    ret = PROP_NAME_MAX - strlen(key);
366    if (ret < 0) {
367        ERROR("Verified property name is too long");
368        return -1;
369    }
370    ret = property_set(key, "1");
371    if (ret < 0)
372        ERROR("Error setting verified property %s: %d", key, ret);
373    free(key);
374    return ret;
375}
376
377int fs_mgr_setup_verity(struct fstab_rec *fstab) {
378
379    int retval = -1;
380    int fd = -1;
381
382    char *verity_blk_name = 0;
383    char *verity_table = 0;
384    char *verity_table_signature = 0;
385
386    char buffer[DM_BUF_SIZE];
387    struct dm_ioctl *io = (struct dm_ioctl *) buffer;
388    char *mount_point = basename(fstab->mount_point);
389
390    // set the dm_ioctl flags
391    io->flags |= 1;
392    io->target_count = 1;
393
394    // check to ensure that the verity device is ext4
395    // TODO: support non-ext4 filesystems
396    if (strcmp(fstab->fs_type, "ext4")) {
397        ERROR("Cannot verify non-ext4 device (%s)", fstab->fs_type);
398        return retval;
399    }
400
401    // read the verity block at the end of the block device
402    // send error code up the chain so we can detect attempts to disable verity
403    retval = read_verity_metadata(fstab->blk_device,
404                                  &verity_table_signature,
405                                  &verity_table);
406    if (retval < 0) {
407        goto out;
408    }
409
410    // get the device mapper fd
411    if ((fd = open("/dev/device-mapper", O_RDWR)) < 0) {
412        ERROR("Error opening device mapper (%s)", strerror(errno));
413        goto out;
414    }
415
416    // create the device
417    if (create_verity_device(io, mount_point, fd) < 0) {
418        ERROR("Couldn't create verity device!");
419        goto out;
420    }
421
422    // get the name of the device file
423    if (get_verity_device_name(io, mount_point, fd, &verity_blk_name) < 0) {
424        ERROR("Couldn't get verity device number!");
425        goto out;
426    }
427
428    // verify the signature on the table
429    if (verify_table(verity_table_signature,
430                            verity_table,
431                            strlen(verity_table)) < 0) {
432        goto out;
433    }
434
435    // load the verity mapping table
436    if (load_verity_table(io, mount_point, fstab->blk_device, fd, verity_table) < 0) {
437        goto out;
438    }
439
440    // activate the device
441    if (resume_verity_table(io, mount_point, fd) < 0) {
442        goto out;
443    }
444
445    // assign the new verity block device as the block device
446    free(fstab->blk_device);
447    fstab->blk_device = verity_blk_name;
448    verity_blk_name = 0;
449
450    // make sure we've set everything up properly
451    if (test_access(fstab->blk_device) < 0) {
452        goto out;
453    }
454
455    // set the property indicating that the partition is verified
456    retval = set_verified_property(mount_point);
457
458out:
459    if (fd != -1) {
460        close(fd);
461    }
462
463    free(verity_table);
464    free(verity_table_signature);
465    free(verity_blk_name);
466
467    return retval;
468}
469