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[thirdparty/systemd.git] / src / home / homework-fscrypt.c
1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2
3 #include <linux/fs.h>
4 #include <openssl/evp.h>
5 #include <openssl/sha.h>
6 #include <sys/ioctl.h>
7 #include <sys/xattr.h>
8
9 #include "errno-util.h"
10 #include "fd-util.h"
11 #include "hexdecoct.h"
12 #include "homework-fscrypt.h"
13 #include "homework-quota.h"
14 #include "memory-util.h"
15 #include "missing_keyctl.h"
16 #include "missing_syscall.h"
17 #include "mkdir.h"
18 #include "nulstr-util.h"
19 #include "openssl-util.h"
20 #include "parse-util.h"
21 #include "process-util.h"
22 #include "random-util.h"
23 #include "rm-rf.h"
24 #include "stdio-util.h"
25 #include "strv.h"
26 #include "tmpfile-util.h"
27 #include "user-util.h"
28 #include "xattr-util.h"
29
30 static int fscrypt_upload_volume_key(
31 const uint8_t key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
32 const void *volume_key,
33 size_t volume_key_size,
34 key_serial_t where) {
35
36 _cleanup_free_ char *hex = NULL;
37 const char *description;
38 struct fscrypt_key key;
39 key_serial_t serial;
40
41 assert(key_descriptor);
42 assert(volume_key);
43 assert(volume_key_size > 0);
44
45 if (volume_key_size > sizeof(key.raw))
46 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Volume key too long.");
47
48 hex = hexmem(key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
49 if (!hex)
50 return log_oom();
51
52 description = strjoina("fscrypt:", hex);
53
54 key = (struct fscrypt_key) {
55 .size = volume_key_size,
56 };
57 memcpy(key.raw, volume_key, volume_key_size);
58
59 /* Upload to the kernel */
60 serial = add_key("logon", description, &key, sizeof(key), where);
61 explicit_bzero_safe(&key, sizeof(key));
62
63 if (serial < 0)
64 return log_error_errno(errno, "Failed to install master key in keyring: %m");
65
66 log_info("Uploaded encryption key to kernel.");
67
68 return 0;
69 }
70
71 static void calculate_key_descriptor(
72 const void *key,
73 size_t key_size,
74 uint8_t ret_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE]) {
75
76 uint8_t hashed[512 / 8] = {}, hashed2[512 / 8] = {};
77
78 /* Derive the key descriptor from the volume key via double SHA512, in order to be compatible with e4crypt */
79
80 assert_se(SHA512(key, key_size, hashed) == hashed);
81 assert_se(SHA512(hashed, sizeof(hashed), hashed2) == hashed2);
82
83 assert_cc(sizeof(hashed2) >= FS_KEY_DESCRIPTOR_SIZE);
84
85 memcpy(ret_key_descriptor, hashed2, FS_KEY_DESCRIPTOR_SIZE);
86 }
87
88 static int fscrypt_slot_try_one(
89 const char *password,
90 const void *salt, size_t salt_size,
91 const void *encrypted, size_t encrypted_size,
92 const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
93 void **ret_decrypted, size_t *ret_decrypted_size) {
94
95
96 _cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
97 _cleanup_(erase_and_freep) void *decrypted = NULL;
98 uint8_t key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
99 int decrypted_size_out1, decrypted_size_out2;
100 uint8_t derived[512 / 8] = {};
101 size_t decrypted_size;
102 const EVP_CIPHER *cc;
103 int r;
104
105 assert(password);
106 assert(salt);
107 assert(salt_size > 0);
108 assert(encrypted);
109 assert(encrypted_size > 0);
110 assert(match_key_descriptor);
111
112 /* Our construction is like this:
113 *
114 * 1. In each key slot we store a salt value plus the encrypted volume key
115 *
116 * 2. Unlocking is via calculating PBKDF2-HMAC-SHA512 of the supplied password (in combination with
117 * the salt), then using the first 256 bit of the hash as key for decrypting the encrypted
118 * volume key in AES256 counter mode.
119 *
120 * 3. Writing a password is similar: calculate PBKDF2-HMAC-SHA512 of the supplied password (in
121 * combination with the salt), then encrypt the volume key in AES256 counter mode with the
122 * resulting hash.
123 */
124
125 if (PKCS5_PBKDF2_HMAC(
126 password, strlen(password),
127 salt, salt_size,
128 0xFFFF, EVP_sha512(),
129 sizeof(derived), derived) != 1) {
130 r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
131 goto finish;
132 }
133
134 context = EVP_CIPHER_CTX_new();
135 if (!context) {
136 r = log_oom();
137 goto finish;
138 }
139
140 /* We use AES256 in counter mode */
141 assert_se(cc = EVP_aes_256_ctr());
142
143 /* We only use the first half of the derived key */
144 assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
145
146 if (EVP_DecryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
147 r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize decryption context.");
148 goto finish;
149 }
150
151 /* Flush out the derived key now, we don't need it anymore */
152 explicit_bzero_safe(derived, sizeof(derived));
153
154 decrypted_size = encrypted_size + EVP_CIPHER_key_length(cc) * 2;
155 decrypted = malloc(decrypted_size);
156 if (!decrypted)
157 return log_oom();
158
159 if (EVP_DecryptUpdate(context, (uint8_t*) decrypted, &decrypted_size_out1, encrypted, encrypted_size) != 1)
160 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to decrypt volume key.");
161
162 assert((size_t) decrypted_size_out1 <= decrypted_size);
163
164 if (EVP_DecryptFinal_ex(context, (uint8_t*) decrypted_size + decrypted_size_out1, &decrypted_size_out2) != 1)
165 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish decryption of volume key.");
166
167 assert((size_t) decrypted_size_out1 + (size_t) decrypted_size_out2 < decrypted_size);
168 decrypted_size = (size_t) decrypted_size_out1 + (size_t) decrypted_size_out2;
169
170 calculate_key_descriptor(decrypted, decrypted_size, key_descriptor);
171
172 if (memcmp(key_descriptor, match_key_descriptor, FS_KEY_DESCRIPTOR_SIZE) != 0)
173 return -ENOANO; /* don't log here */
174
175 r = fscrypt_upload_volume_key(key_descriptor, decrypted, decrypted_size, KEY_SPEC_THREAD_KEYRING);
176 if (r < 0)
177 return r;
178
179 if (ret_decrypted)
180 *ret_decrypted = TAKE_PTR(decrypted);
181 if (ret_decrypted_size)
182 *ret_decrypted_size = decrypted_size;
183
184 return 0;
185
186 finish:
187 explicit_bzero_safe(derived, sizeof(derived));
188 return r;
189 }
190
191 static int fscrypt_slot_try_many(
192 char **passwords,
193 const void *salt, size_t salt_size,
194 const void *encrypted, size_t encrypted_size,
195 const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
196 void **ret_decrypted, size_t *ret_decrypted_size) {
197
198 char **i;
199 int r;
200
201 STRV_FOREACH(i, passwords) {
202 r = fscrypt_slot_try_one(*i, salt, salt_size, encrypted, encrypted_size, match_key_descriptor, ret_decrypted, ret_decrypted_size);
203 if (r != -ENOANO)
204 return r;
205 }
206
207 return -ENOANO;
208 }
209
210 static int fscrypt_setup(
211 const PasswordCache *cache,
212 char **password,
213 HomeSetup *setup,
214 void **ret_volume_key,
215 size_t *ret_volume_key_size) {
216
217 _cleanup_free_ char *xattr_buf = NULL;
218 const char *xa;
219 int r;
220
221 assert(setup);
222 assert(setup->root_fd >= 0);
223
224 r = flistxattr_malloc(setup->root_fd, &xattr_buf);
225 if (r < 0)
226 return log_error_errno(errno, "Failed to retrieve xattr list: %m");
227
228 NULSTR_FOREACH(xa, xattr_buf) {
229 _cleanup_free_ void *salt = NULL, *encrypted = NULL;
230 _cleanup_free_ char *value = NULL;
231 size_t salt_size, encrypted_size;
232 const char *nr, *e;
233 char **list;
234 int n;
235
236 /* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
237 nr = startswith(xa, "trusted.fscrypt_slot");
238 if (!nr)
239 continue;
240 if (safe_atou32(nr, NULL) < 0)
241 continue;
242
243 n = fgetxattr_malloc(setup->root_fd, xa, &value);
244 if (n == -ENODATA) /* deleted by now? */
245 continue;
246 if (n < 0)
247 return log_error_errno(n, "Failed to read %s xattr: %m", xa);
248
249 e = memchr(value, ':', n);
250 if (!e)
251 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "xattr %s lacks ':' separator: %m", xa);
252
253 r = unbase64mem(value, e - value, &salt, &salt_size);
254 if (r < 0)
255 return log_error_errno(r, "Failed to decode salt of %s: %m", xa);
256 r = unbase64mem(e+1, n - (e - value) - 1, &encrypted, &encrypted_size);
257 if (r < 0)
258 return log_error_errno(r, "Failed to decode encrypted key of %s: %m", xa);
259
260 r = -ENOANO;
261 FOREACH_POINTER(list, cache->pkcs11_passwords, cache->fido2_passwords, password) {
262 r = fscrypt_slot_try_many(
263 list,
264 salt, salt_size,
265 encrypted, encrypted_size,
266 setup->fscrypt_key_descriptor,
267 ret_volume_key, ret_volume_key_size);
268 if (r != -ENOANO)
269 break;
270 }
271 if (r < 0) {
272 if (r != -ENOANO)
273 return r;
274 } else
275 return 0;
276 }
277
278 return log_error_errno(SYNTHETIC_ERRNO(ENOKEY), "Failed to set up home directory with provided passwords.");
279 }
280
281 int home_setup_fscrypt(
282 UserRecord *h,
283 PasswordCache *cache,
284 HomeSetup *setup) {
285
286 _cleanup_(erase_and_freep) void *volume_key = NULL;
287 struct fscrypt_policy policy = {};
288 size_t volume_key_size = 0;
289 const char *ip;
290 int r;
291
292 assert(h);
293 assert(setup);
294 assert(user_record_storage(h) == USER_FSCRYPT);
295
296 assert_se(ip = user_record_image_path(h));
297
298 setup->root_fd = open(ip, O_RDONLY|O_CLOEXEC|O_DIRECTORY);
299 if (setup->root_fd < 0)
300 return log_error_errno(errno, "Failed to open home directory: %m");
301
302 if (ioctl(setup->root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
303 if (errno == ENODATA)
304 return log_error_errno(errno, "Home directory %s is not encrypted.", ip);
305 if (ERRNO_IS_NOT_SUPPORTED(errno)) {
306 log_error_errno(errno, "File system does not support fscrypt: %m");
307 return -ENOLINK; /* make recognizable */
308 }
309 return log_error_errno(errno, "Failed to acquire encryption policy of %s: %m", ip);
310 }
311
312 memcpy(setup->fscrypt_key_descriptor, policy.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
313
314 r = fscrypt_setup(
315 cache,
316 h->password,
317 setup,
318 &volume_key,
319 &volume_key_size);
320 if (r < 0)
321 return r;
322
323 /* Also install the access key in the user's own keyring */
324
325 if (uid_is_valid(h->uid)) {
326 r = safe_fork("(sd-addkey)",
327 FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_LOG|FORK_WAIT|FORK_REOPEN_LOG,
328 NULL);
329 if (r < 0)
330 return log_error_errno(r, "Failed install encryption key in user's keyring: %m");
331 if (r == 0) {
332 gid_t gid;
333
334 /* Child */
335
336 gid = user_record_gid(h);
337 if (setresgid(gid, gid, gid) < 0) {
338 log_error_errno(errno, "Failed to change GID to " GID_FMT ": %m", gid);
339 _exit(EXIT_FAILURE);
340 }
341
342 if (setgroups(0, NULL) < 0) {
343 log_error_errno(errno, "Failed to reset auxiliary groups list: %m");
344 _exit(EXIT_FAILURE);
345 }
346
347 if (setresuid(h->uid, h->uid, h->uid) < 0) {
348 log_error_errno(errno, "Failed to change UID to " UID_FMT ": %m", h->uid);
349 _exit(EXIT_FAILURE);
350 }
351
352 r = fscrypt_upload_volume_key(
353 setup->fscrypt_key_descriptor,
354 volume_key,
355 volume_key_size,
356 KEY_SPEC_USER_KEYRING);
357 if (r < 0)
358 _exit(EXIT_FAILURE);
359
360 _exit(EXIT_SUCCESS);
361 }
362 }
363
364 return 0;
365 }
366
367 static int fscrypt_slot_set(
368 int root_fd,
369 const void *volume_key,
370 size_t volume_key_size,
371 const char *password,
372 uint32_t nr) {
373
374 _cleanup_free_ char *salt_base64 = NULL, *encrypted_base64 = NULL, *joined = NULL;
375 char label[STRLEN("trusted.fscrypt_slot") + DECIMAL_STR_MAX(nr) + 1];
376 _cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
377 int r, encrypted_size_out1, encrypted_size_out2;
378 uint8_t salt[64], derived[512 / 8] = {};
379 _cleanup_free_ void *encrypted = NULL;
380 const EVP_CIPHER *cc;
381 size_t encrypted_size;
382
383 r = genuine_random_bytes(salt, sizeof(salt), RANDOM_BLOCK);
384 if (r < 0)
385 return log_error_errno(r, "Failed to generate salt: %m");
386
387 if (PKCS5_PBKDF2_HMAC(
388 password, strlen(password),
389 salt, sizeof(salt),
390 0xFFFF, EVP_sha512(),
391 sizeof(derived), derived) != 1) {
392 r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
393 goto finish;
394 }
395
396 context = EVP_CIPHER_CTX_new();
397 if (!context) {
398 r = log_oom();
399 goto finish;
400 }
401
402 /* We use AES256 in counter mode */
403 cc = EVP_aes_256_ctr();
404
405 /* We only use the first half of the derived key */
406 assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
407
408 if (EVP_EncryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
409 r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize encryption context.");
410 goto finish;
411 }
412
413 /* Flush out the derived key now, we don't need it anymore */
414 explicit_bzero_safe(derived, sizeof(derived));
415
416 encrypted_size = volume_key_size + EVP_CIPHER_key_length(cc) * 2;
417 encrypted = malloc(encrypted_size);
418 if (!encrypted)
419 return log_oom();
420
421 if (EVP_EncryptUpdate(context, (uint8_t*) encrypted, &encrypted_size_out1, volume_key, volume_key_size) != 1)
422 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to encrypt volume key.");
423
424 assert((size_t) encrypted_size_out1 <= encrypted_size);
425
426 if (EVP_EncryptFinal_ex(context, (uint8_t*) encrypted_size + encrypted_size_out1, &encrypted_size_out2) != 1)
427 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish encryption of volume key.");
428
429 assert((size_t) encrypted_size_out1 + (size_t) encrypted_size_out2 < encrypted_size);
430 encrypted_size = (size_t) encrypted_size_out1 + (size_t) encrypted_size_out2;
431
432 r = base64mem(salt, sizeof(salt), &salt_base64);
433 if (r < 0)
434 return log_oom();
435
436 r = base64mem(encrypted, encrypted_size, &encrypted_base64);
437 if (r < 0)
438 return log_oom();
439
440 joined = strjoin(salt_base64, ":", encrypted_base64);
441 if (!joined)
442 return log_oom();
443
444 xsprintf(label, "trusted.fscrypt_slot%" PRIu32, nr);
445 if (fsetxattr(root_fd, label, joined, strlen(joined), 0) < 0)
446 return log_error_errno(errno, "Failed to write xattr %s: %m", label);
447
448 log_info("Written key slot %s.", label);
449
450 return 0;
451
452 finish:
453 explicit_bzero_safe(derived, sizeof(derived));
454 return r;
455 }
456
457 int home_create_fscrypt(
458 UserRecord *h,
459 char **effective_passwords,
460 UserRecord **ret_home) {
461
462 _cleanup_(rm_rf_physical_and_freep) char *temporary = NULL;
463 _cleanup_(user_record_unrefp) UserRecord *new_home = NULL;
464 _cleanup_(erase_and_freep) void *volume_key = NULL;
465 struct fscrypt_policy policy = {};
466 size_t volume_key_size = 512 / 8;
467 _cleanup_close_ int root_fd = -1;
468 _cleanup_free_ char *d = NULL;
469 uint32_t nr = 0;
470 const char *ip;
471 char **i;
472 int r;
473
474 assert(h);
475 assert(user_record_storage(h) == USER_FSCRYPT);
476 assert(ret_home);
477
478 assert_se(ip = user_record_image_path(h));
479
480 r = tempfn_random(ip, "homework", &d);
481 if (r < 0)
482 return log_error_errno(r, "Failed to allocate temporary directory: %m");
483
484 (void) mkdir_parents(d, 0755);
485
486 if (mkdir(d, 0700) < 0)
487 return log_error_errno(errno, "Failed to create temporary home directory %s: %m", d);
488
489 temporary = TAKE_PTR(d); /* Needs to be destroyed now */
490
491 root_fd = open(temporary, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
492 if (root_fd < 0)
493 return log_error_errno(errno, "Failed to open temporary home directory: %m");
494
495 if (ioctl(root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
496 if (ERRNO_IS_NOT_SUPPORTED(errno)) {
497 log_error_errno(errno, "File system does not support fscrypt: %m");
498 return -ENOLINK; /* make recognizable */
499 }
500 if (errno != ENODATA)
501 return log_error_errno(errno, "Failed to get fscrypt policy of directory: %m");
502 } else
503 return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Parent of %s already encrypted, refusing.", d);
504
505 volume_key = malloc(volume_key_size);
506 if (!volume_key)
507 return log_oom();
508
509 r = genuine_random_bytes(volume_key, volume_key_size, RANDOM_BLOCK);
510 if (r < 0)
511 return log_error_errno(r, "Failed to acquire volume key: %m");
512
513 log_info("Generated volume key of size %zu.", volume_key_size);
514
515 policy = (struct fscrypt_policy) {
516 .contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS,
517 .filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS,
518 .flags = FS_POLICY_FLAGS_PAD_32,
519 };
520
521 calculate_key_descriptor(volume_key, volume_key_size, policy.master_key_descriptor);
522
523 r = fscrypt_upload_volume_key(policy.master_key_descriptor, volume_key, volume_key_size, KEY_SPEC_THREAD_KEYRING);
524 if (r < 0)
525 return r;
526
527 log_info("Uploaded volume key to kernel.");
528
529 if (ioctl(root_fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) < 0)
530 return log_error_errno(errno, "Failed to set fscrypt policy on directory: %m");
531
532 log_info("Encryption policy set.");
533
534 STRV_FOREACH(i, effective_passwords) {
535 r = fscrypt_slot_set(root_fd, volume_key, volume_key_size, *i, nr);
536 if (r < 0)
537 return r;
538
539 nr++;
540 }
541
542 (void) home_update_quota_classic(h, temporary);
543
544 r = home_populate(h, root_fd);
545 if (r < 0)
546 return r;
547
548 r = home_sync_and_statfs(root_fd, NULL);
549 if (r < 0)
550 return r;
551
552 r = user_record_clone(h, USER_RECORD_LOAD_MASK_SECRET|USER_RECORD_PERMISSIVE, &new_home);
553 if (r < 0)
554 return log_error_errno(r, "Failed to clone record: %m");
555
556 r = user_record_add_binding(
557 new_home,
558 USER_FSCRYPT,
559 ip,
560 SD_ID128_NULL,
561 SD_ID128_NULL,
562 SD_ID128_NULL,
563 NULL,
564 NULL,
565 UINT64_MAX,
566 NULL,
567 NULL,
568 h->uid,
569 (gid_t) h->uid);
570 if (r < 0)
571 return log_error_errno(r, "Failed to add binding to record: %m");
572
573 if (rename(temporary, ip) < 0)
574 return log_error_errno(errno, "Failed to rename %s to %s: %m", temporary, ip);
575
576 temporary = mfree(temporary);
577
578 log_info("Everything completed.");
579
580 *ret_home = TAKE_PTR(new_home);
581 return 0;
582 }
583
584 int home_passwd_fscrypt(
585 UserRecord *h,
586 HomeSetup *setup,
587 PasswordCache *cache, /* the passwords acquired via PKCS#11/FIDO2 security tokens */
588 char **effective_passwords /* new passwords */) {
589
590 _cleanup_(erase_and_freep) void *volume_key = NULL;
591 _cleanup_free_ char *xattr_buf = NULL;
592 size_t volume_key_size = 0;
593 uint32_t slot = 0;
594 const char *xa;
595 char **p;
596 int r;
597
598 assert(h);
599 assert(user_record_storage(h) == USER_FSCRYPT);
600 assert(setup);
601
602 r = fscrypt_setup(
603 cache,
604 h->password,
605 setup,
606 &volume_key,
607 &volume_key_size);
608 if (r < 0)
609 return r;
610
611 STRV_FOREACH(p, effective_passwords) {
612 r = fscrypt_slot_set(setup->root_fd, volume_key, volume_key_size, *p, slot);
613 if (r < 0)
614 return r;
615
616 slot++;
617 }
618
619 r = flistxattr_malloc(setup->root_fd, &xattr_buf);
620 if (r < 0)
621 return log_error_errno(errno, "Failed to retrieve xattr list: %m");
622
623 NULSTR_FOREACH(xa, xattr_buf) {
624 const char *nr;
625 uint32_t z;
626
627 /* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
628 nr = startswith(xa, "trusted.fscrypt_slot");
629 if (!nr)
630 continue;
631 if (safe_atou32(nr, &z) < 0)
632 continue;
633
634 if (z < slot)
635 continue;
636
637 if (fremovexattr(setup->root_fd, xa) < 0)
638
639 if (errno != ENODATA)
640 log_warning_errno(errno, "Failed to remove xattr %s: %m", xa);
641 }
642
643 return 0;
644 }
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