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db9ecf05 | 1 | /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
6e200d55 | 2 | |
6e200d55 | 3 | #include <errno.h> |
07630cea | 4 | #include <fcntl.h> |
0d0c6639 | 5 | #include <getopt.h> |
26ded557 | 6 | #include <linux/random.h> |
26ded557 LP |
7 | #include <sys/ioctl.h> |
8 | #if USE_SYS_RANDOM_H | |
9 | # include <sys/random.h> | |
10 | #endif | |
6e200d55 | 11 | #include <sys/stat.h> |
26ded557 | 12 | #include <sys/xattr.h> |
07630cea | 13 | #include <unistd.h> |
6e200d55 | 14 | |
8ba12aef LP |
15 | #include "sd-id128.h" |
16 | ||
b5efdb8a | 17 | #include "alloc-util.h" |
d6b4d1c7 | 18 | #include "build.h" |
3ffd4af2 | 19 | #include "fd-util.h" |
4b3b5bc7 | 20 | #include "fs-util.h" |
c004493c | 21 | #include "io-util.h" |
6e200d55 | 22 | #include "log.h" |
5e332028 | 23 | #include "main-func.h" |
123aeae2 | 24 | #include "missing_random.h" |
f5947a5e | 25 | #include "missing_syscall.h" |
49e942b2 | 26 | #include "mkdir.h" |
26ded557 | 27 | #include "parse-util.h" |
0d0c6639 | 28 | #include "pretty-print.h" |
3e155eba | 29 | #include "random-util.h" |
0d0c6639 | 30 | #include "string-table.h" |
07630cea | 31 | #include "string-util.h" |
bf819d3a | 32 | #include "sync-util.h" |
da2862ef | 33 | #include "sha256.h" |
26ded557 LP |
34 | #include "xattr-util.h" |
35 | ||
0d0c6639 FB |
36 | typedef enum SeedAction { |
37 | ACTION_LOAD, | |
38 | ACTION_SAVE, | |
39 | _ACTION_MAX, | |
40 | _ACTION_INVALID = -EINVAL, | |
41 | } SeedAction; | |
42 | ||
26ded557 LP |
43 | typedef enum CreditEntropy { |
44 | CREDIT_ENTROPY_NO_WAY, | |
45 | CREDIT_ENTROPY_YES_PLEASE, | |
46 | CREDIT_ENTROPY_YES_FORCED, | |
47 | } CreditEntropy; | |
48 | ||
0d0c6639 FB |
49 | static SeedAction arg_action = _ACTION_INVALID; |
50 | ||
26ded557 LP |
51 | static CreditEntropy may_credit(int seed_fd) { |
52 | _cleanup_free_ char *creditable = NULL; | |
53 | const char *e; | |
54 | int r; | |
55 | ||
56 | assert(seed_fd >= 0); | |
57 | ||
58 | e = getenv("SYSTEMD_RANDOM_SEED_CREDIT"); | |
59 | if (!e) { | |
60 | log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is not set, not crediting entropy."); | |
61 | return CREDIT_ENTROPY_NO_WAY; | |
62 | } | |
63 | if (streq(e, "force")) { | |
64 | log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is set to 'force', crediting entropy."); | |
65 | return CREDIT_ENTROPY_YES_FORCED; | |
66 | } | |
67 | ||
68 | r = parse_boolean(e); | |
69 | if (r <= 0) { | |
70 | if (r < 0) | |
71 | log_warning_errno(r, "Failed to parse $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy: %m"); | |
72 | else | |
73 | log_debug("Crediting entropy is turned off via $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy."); | |
74 | ||
75 | return CREDIT_ENTROPY_NO_WAY; | |
76 | } | |
77 | ||
78 | /* Determine if the file is marked as creditable */ | |
79 | r = fgetxattr_malloc(seed_fd, "user.random-seed-creditable", &creditable); | |
80 | if (r < 0) { | |
00675c36 | 81 | if (ERRNO_IS_XATTR_ABSENT(r)) |
26ded557 LP |
82 | log_debug_errno(r, "Seed file is not marked as creditable, not crediting."); |
83 | else | |
84 | log_warning_errno(r, "Failed to read extended attribute, ignoring: %m"); | |
85 | ||
86 | return CREDIT_ENTROPY_NO_WAY; | |
87 | } | |
88 | ||
89 | r = parse_boolean(creditable); | |
90 | if (r <= 0) { | |
91 | if (r < 0) | |
92 | log_warning_errno(r, "Failed to parse user.random-seed-creditable extended attribute, ignoring: %s", creditable); | |
93 | else | |
94 | log_debug("Seed file is marked as not creditable, not crediting."); | |
95 | ||
96 | return CREDIT_ENTROPY_NO_WAY; | |
97 | } | |
98 | ||
99 | /* Don't credit the random seed if we are in first-boot mode, because we are supposed to start from | |
100 | * scratch. This is a safety precaution for cases where we people ship "golden" images with empty | |
101 | * /etc but populated /var that contains a random seed. */ | |
249d31b0 FB |
102 | r = RET_NERRNO(access("/run/systemd/first-boot", F_OK)); |
103 | if (r == -ENOENT) | |
104 | /* All is good, we are not in first-boot mode. */ | |
105 | return CREDIT_ENTROPY_YES_PLEASE; | |
106 | if (r < 0) { | |
107 | log_warning_errno(r, "Failed to check whether we are in first-boot mode, not crediting entropy: %m"); | |
26ded557 LP |
108 | return CREDIT_ENTROPY_NO_WAY; |
109 | } | |
110 | ||
249d31b0 FB |
111 | log_debug("Not crediting entropy, since booted in first-boot mode."); |
112 | return CREDIT_ENTROPY_NO_WAY; | |
26ded557 | 113 | } |
6e200d55 | 114 | |
205138d8 FB |
115 | static int random_seed_size(int seed_fd, size_t *ret_size) { |
116 | struct stat st; | |
117 | ||
118 | assert(ret_size); | |
119 | assert(seed_fd >= 0); | |
120 | ||
121 | if (fstat(seed_fd, &st) < 0) | |
122 | return log_error_errno(errno, "Failed to stat() seed file " RANDOM_SEED ": %m"); | |
123 | ||
124 | /* If the seed file is larger than what the kernel expects, then honour the existing size and | |
125 | * save/restore as much as it says */ | |
126 | ||
127 | *ret_size = CLAMP((uint64_t)st.st_size, random_pool_size(), RANDOM_POOL_SIZE_MAX); | |
128 | return 0; | |
129 | } | |
130 | ||
a2f0dbb8 FB |
131 | static void load_machine_id(int urandom_fd) { |
132 | sd_id128_t mid; | |
133 | int r; | |
134 | ||
135 | assert(urandom_fd >= 0); | |
136 | ||
137 | /* As an extra protection against "golden images" that are put together sloppily, i.e. images which | |
138 | * are duplicated on multiple systems but where the random seed file is not properly | |
139 | * reset. Frequently the machine ID is properly reset on those systems however (simply because it's | |
140 | * easier to notice, if it isn't due to address clashes and so on, while random seed equivalence is | |
141 | * generally not noticed easily), hence let's simply write the machined ID into the random pool | |
142 | * too. */ | |
143 | r = sd_id128_get_machine(&mid); | |
144 | if (r < 0) | |
145 | return (void) log_debug_errno(r, "Failed to get machine ID, ignoring: %m"); | |
146 | ||
147 | r = random_write_entropy(urandom_fd, &mid, sizeof(mid), /* credit= */ false); | |
148 | if (r < 0) | |
149 | log_debug_errno(r, "Failed to write machine ID to /dev/urandom, ignoring: %m"); | |
150 | } | |
151 | ||
d3fa881a FB |
152 | static int load_seed_file( |
153 | int seed_fd, | |
154 | int urandom_fd, | |
155 | size_t seed_size, | |
156 | struct sha256_ctx **ret_hash_state) { | |
157 | ||
158 | _cleanup_free_ void *buf = NULL; | |
159 | CreditEntropy lets_credit; | |
d3fa881a FB |
160 | ssize_t k; |
161 | int r; | |
162 | ||
163 | assert(seed_fd >= 0); | |
164 | assert(urandom_fd >= 0); | |
165 | ||
d3fa881a FB |
166 | buf = malloc(seed_size); |
167 | if (!buf) | |
168 | return log_oom(); | |
169 | ||
170 | k = loop_read(seed_fd, buf, seed_size, false); | |
171 | if (k < 0) { | |
ea37e1ed | 172 | log_warning_errno(k, "Failed to read seed from " RANDOM_SEED ": %m"); |
d3fa881a FB |
173 | return 0; |
174 | } | |
175 | if (k == 0) { | |
176 | log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding."); | |
177 | return 0; | |
178 | } | |
179 | ||
180 | /* If we're going to later write out a seed file, initialize a hash state with the contents of the | |
181 | * seed file we just read, so that the new one can't regress in entropy. */ | |
182 | if (ret_hash_state) { | |
183 | struct sha256_ctx *hash_state; | |
184 | ||
f913c784 | 185 | hash_state = new(struct sha256_ctx, 1); |
d3fa881a FB |
186 | if (!hash_state) |
187 | return log_oom(); | |
188 | ||
189 | sha256_init_ctx(hash_state); | |
a16c65f3 | 190 | sha256_process_bytes_and_size(buf, k, hash_state); /* Hash with length to distinguish from new seed. */ |
d3fa881a FB |
191 | |
192 | *ret_hash_state = hash_state; | |
193 | } | |
194 | ||
195 | (void) lseek(seed_fd, 0, SEEK_SET); | |
196 | ||
197 | lets_credit = may_credit(seed_fd); | |
198 | ||
199 | /* Before we credit or use the entropy, let's make sure to securely drop the creditable xattr from | |
200 | * the file, so that we never credit the same random seed again. Note that further down we'll write a | |
201 | * new seed again, and likely mark it as credible again, hence this is just paranoia to close the | |
202 | * short time window between the time we upload the random seed into the kernel and download the new | |
203 | * one from it. */ | |
204 | ||
205 | if (fremovexattr(seed_fd, "user.random-seed-creditable") < 0) { | |
206 | if (!ERRNO_IS_XATTR_ABSENT(errno)) | |
207 | log_warning_errno(errno, "Failed to remove extended attribute, ignoring: %m"); | |
208 | ||
209 | /* Otherwise, there was no creditable flag set, which is OK. */ | |
210 | } else { | |
211 | r = fsync_full(seed_fd); | |
212 | if (r < 0) { | |
213 | log_warning_errno(r, "Failed to synchronize seed to disk, not crediting entropy: %m"); | |
214 | ||
215 | if (lets_credit == CREDIT_ENTROPY_YES_PLEASE) | |
216 | lets_credit = CREDIT_ENTROPY_NO_WAY; | |
217 | } | |
218 | } | |
219 | ||
220 | r = random_write_entropy(urandom_fd, buf, k, | |
221 | IN_SET(lets_credit, CREDIT_ENTROPY_YES_PLEASE, CREDIT_ENTROPY_YES_FORCED)); | |
222 | if (r < 0) | |
ea37e1ed | 223 | log_warning_errno(r, "Failed to write seed to /dev/urandom: %m"); |
d3fa881a FB |
224 | |
225 | return 0; | |
226 | } | |
227 | ||
228 | static int save_seed_file( | |
229 | int seed_fd, | |
230 | int urandom_fd, | |
231 | size_t seed_size, | |
232 | bool synchronous, | |
233 | struct sha256_ctx *hash_state) { | |
234 | ||
235 | _cleanup_free_ void *buf = NULL; | |
236 | bool getrandom_worked = false; | |
237 | ssize_t k, l; | |
238 | int r; | |
239 | ||
240 | assert(seed_fd >= 0); | |
241 | assert(urandom_fd >= 0); | |
242 | ||
243 | /* This is just a safety measure. Given that we are root and most likely created the file ourselves | |
244 | * the mode and owner should be correct anyway. */ | |
245 | r = fchmod_and_chown(seed_fd, 0600, 0, 0); | |
246 | if (r < 0) | |
247 | return log_error_errno(r, "Failed to adjust seed file ownership and access mode: %m"); | |
248 | ||
249 | buf = malloc(seed_size); | |
250 | if (!buf) | |
251 | return log_oom(); | |
252 | ||
d3fa881a FB |
253 | k = getrandom(buf, seed_size, GRND_NONBLOCK); |
254 | if (k < 0 && errno == EAGAIN && synchronous) { | |
46e0b5dc FB |
255 | /* If we're asked to make ourselves a barrier for proper initialization of the random pool |
256 | * make this whole job synchronous by asking getrandom() to wait until the requested number | |
257 | * of random bytes is available. */ | |
d3fa881a | 258 | log_notice("Kernel entropy pool is not initialized yet, waiting until it is."); |
46e0b5dc | 259 | k = getrandom(buf, seed_size, 0); |
d3fa881a FB |
260 | } |
261 | if (k < 0) | |
262 | log_debug_errno(errno, "Failed to read random data with getrandom(), falling back to /dev/urandom: %m"); | |
263 | else if ((size_t) k < seed_size) | |
264 | log_debug("Short read from getrandom(), falling back to /dev/urandom."); | |
265 | else | |
266 | getrandom_worked = true; | |
267 | ||
268 | if (!getrandom_worked) { | |
269 | /* Retry with classic /dev/urandom */ | |
270 | k = loop_read(urandom_fd, buf, seed_size, false); | |
271 | if (k < 0) | |
272 | return log_error_errno(k, "Failed to read new seed from /dev/urandom: %m"); | |
273 | if (k == 0) | |
274 | return log_error_errno(SYNTHETIC_ERRNO(EIO), "Got EOF while reading from /dev/urandom."); | |
275 | } | |
276 | ||
277 | /* If we previously read in a seed file, then hash the new seed into the old one, and replace the | |
278 | * last 32 bytes of the seed with the hash output, so that the new seed file can't regress in | |
279 | * entropy. */ | |
280 | if (hash_state) { | |
281 | uint8_t hash[SHA256_DIGEST_SIZE]; | |
282 | ||
a16c65f3 | 283 | sha256_process_bytes_and_size(buf, k, hash_state); /* Hash with length to distinguish from old seed. */ |
d3fa881a FB |
284 | sha256_finish_ctx(hash_state, hash); |
285 | l = MIN((size_t)k, sizeof(hash)); | |
286 | memcpy((uint8_t *)buf + k - l, hash, l); | |
287 | } | |
288 | ||
289 | r = loop_write(seed_fd, buf, (size_t) k, false); | |
290 | if (r < 0) | |
291 | return log_error_errno(r, "Failed to write new random seed file: %m"); | |
292 | ||
293 | if (ftruncate(seed_fd, k) < 0) | |
294 | return log_error_errno(r, "Failed to truncate random seed file: %m"); | |
295 | ||
296 | r = fsync_full(seed_fd); | |
297 | if (r < 0) | |
298 | return log_error_errno(r, "Failed to synchronize seed file: %m"); | |
299 | ||
300 | /* If we got this random seed data from getrandom() the data is suitable for crediting entropy later | |
301 | * on. Let's keep that in mind by setting an extended attribute. on the file */ | |
302 | if (getrandom_worked) | |
303 | if (fsetxattr(seed_fd, "user.random-seed-creditable", "1", 1, 0) < 0) | |
304 | log_full_errno(ERRNO_IS_NOT_SUPPORTED(errno) ? LOG_DEBUG : LOG_WARNING, errno, | |
305 | "Failed to mark seed file as creditable, ignoring: %m"); | |
306 | return 0; | |
307 | } | |
308 | ||
0d0c6639 FB |
309 | static int help(int argc, char *argv[], void *userdata) { |
310 | _cleanup_free_ char *link = NULL; | |
311 | int r; | |
312 | ||
313 | r = terminal_urlify_man("systemd-random-seed", "8", &link); | |
314 | if (r < 0) | |
315 | return log_oom(); | |
316 | ||
317 | printf("%1$s [OPTIONS...] COMMAND\n" | |
318 | "\n%5$sLoad and save the system random seed at boot and shutdown.%6$s\n" | |
319 | "\n%3$sCommands:%4$s\n" | |
320 | " load Load a random seed saved on disk into the kernel entropy pool\n" | |
321 | " save Save a new random seed on disk\n" | |
322 | "\n%3$sOptions:%4$s\n" | |
323 | " -h --help Show this help\n" | |
324 | " --version Show package version\n" | |
325 | "\nSee the %2$s for details.\n", | |
326 | program_invocation_short_name, | |
327 | link, | |
328 | ansi_underline(), | |
329 | ansi_normal(), | |
330 | ansi_highlight(), | |
331 | ansi_normal()); | |
332 | ||
333 | return 0; | |
334 | } | |
335 | ||
336 | static const char* const seed_action_table[_ACTION_MAX] = { | |
337 | [ACTION_LOAD] = "load", | |
338 | [ACTION_SAVE] = "save", | |
339 | }; | |
340 | ||
341 | DEFINE_PRIVATE_STRING_TABLE_LOOKUP_FROM_STRING(seed_action, SeedAction); | |
342 | ||
343 | static int parse_argv(int argc, char *argv[]) { | |
344 | enum { | |
345 | ARG_VERSION = 0x100, | |
346 | }; | |
347 | ||
348 | static const struct option options[] = { | |
349 | { "help", no_argument, NULL, 'h' }, | |
350 | { "version", no_argument, NULL, ARG_VERSION }, | |
351 | }; | |
352 | ||
353 | int c; | |
354 | ||
355 | assert(argc >= 0); | |
356 | assert(argv); | |
357 | ||
358 | while ((c = getopt_long(argc, argv, "h", options, NULL)) >= 0) | |
359 | switch (c) { | |
360 | case 'h': | |
361 | return help(0, NULL, NULL); | |
362 | case ARG_VERSION: | |
363 | return version(); | |
364 | case '?': | |
365 | return -EINVAL; | |
366 | ||
367 | default: | |
368 | assert_not_reached(); | |
369 | } | |
370 | ||
371 | if (optind + 1 != argc) | |
372 | return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "This program requires one argument."); | |
373 | ||
374 | arg_action = seed_action_from_string(argv[optind]); | |
375 | if (arg_action < 0) | |
376 | return log_error_errno(arg_action, "Unknown action '%s'", argv[optind]); | |
377 | ||
378 | return 1; | |
379 | } | |
380 | ||
72d0d7a6 | 381 | static int run(int argc, char *argv[]) { |
d3fa881a | 382 | _cleanup_free_ struct sha256_ctx *hash_state = NULL; |
254d1313 | 383 | _cleanup_close_ int seed_fd = -EBADF, random_fd = -EBADF; |
d3fa881a FB |
384 | bool read_seed_file, write_seed_file, synchronous; |
385 | size_t seed_size; | |
ac93390b | 386 | int r; |
6e200d55 | 387 | |
d2acb93d | 388 | log_setup(); |
6e200d55 | 389 | |
0d0c6639 FB |
390 | r = parse_argv(argc, argv); |
391 | if (r <= 0) | |
392 | return r; | |
72d0d7a6 | 393 | |
4c12626c LP |
394 | umask(0022); |
395 | ||
5468d9af | 396 | r = mkdir_parents(RANDOM_SEED, 0755); |
72d0d7a6 ZJS |
397 | if (r < 0) |
398 | return log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m"); | |
b56e5747 | 399 | |
f913c784 JD |
400 | random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY); |
401 | if (random_fd < 0) | |
402 | return log_error_errno(errno, "Failed to open /dev/urandom: %m"); | |
403 | ||
0d0c6639 FB |
404 | /* When we load the seed we read it and write it to the device and then immediately update the saved |
405 | * seed with new data, to make sure the next boot gets seeded differently. */ | |
6e200d55 | 406 | |
0d0c6639 FB |
407 | switch (arg_action) { |
408 | case ACTION_LOAD: | |
a2f0dbb8 FB |
409 | /* First, let's write the machine ID into /dev/urandom, not crediting entropy. See |
410 | * load_machine_id() for an explanation why. */ | |
411 | load_machine_id(random_fd); | |
412 | ||
ce179470 LP |
413 | seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
414 | if (seed_fd < 0) { | |
15d961bf LP |
415 | int open_rw_error = -errno; |
416 | ||
ac93390b | 417 | write_seed_file = false; |
8edc2d22 | 418 | |
ce179470 LP |
419 | seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY); |
420 | if (seed_fd < 0) { | |
8edc2d22 | 421 | bool missing = errno == ENOENT; |
3f6fbfe6 | 422 | int level = missing ? LOG_DEBUG : LOG_ERR; |
8edc2d22 | 423 | |
3f6fbfe6 FB |
424 | log_full_errno(level, open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m"); |
425 | log_full_errno(level, errno, "Failed to open " RANDOM_SEED " for reading: %m"); | |
29d487ad | 426 | return missing ? 0 : -errno; |
6e200d55 | 427 | } |
ac93390b LP |
428 | } else |
429 | write_seed_file = true; | |
6e200d55 | 430 | |
ac93390b | 431 | read_seed_file = true; |
26ded557 | 432 | synchronous = true; /* make this invocation a synchronous barrier for random pool initialization */ |
0d0c6639 | 433 | break; |
6e200d55 | 434 | |
0d0c6639 | 435 | case ACTION_SAVE: |
ce179470 | 436 | seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
72d0d7a6 ZJS |
437 | if (seed_fd < 0) |
438 | return log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m"); | |
6e200d55 | 439 | |
ac93390b LP |
440 | read_seed_file = false; |
441 | write_seed_file = true; | |
26ded557 | 442 | synchronous = false; |
0d0c6639 FB |
443 | break; |
444 | ||
445 | default: | |
446 | assert_not_reached(); | |
447 | } | |
6e200d55 | 448 | |
d3fa881a | 449 | r = random_seed_size(seed_fd, &seed_size); |
205138d8 FB |
450 | if (r < 0) |
451 | return r; | |
ac93390b | 452 | |
29d487ad | 453 | if (read_seed_file) |
d3fa881a FB |
454 | r = load_seed_file(seed_fd, random_fd, seed_size, |
455 | write_seed_file ? &hash_state : NULL); | |
26ded557 | 456 | |
d3fa881a FB |
457 | if (r >= 0 && write_seed_file) |
458 | r = save_seed_file(seed_fd, random_fd, seed_size, synchronous, hash_state); | |
26ded557 | 459 | |
d3fa881a | 460 | return r; |
6e200d55 | 461 | } |
72d0d7a6 ZJS |
462 | |
463 | DEFINE_MAIN_FUNCTION(run); |