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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> |
26ded557 | 5 | #include <linux/random.h> |
26ded557 LP |
6 | #include <sys/ioctl.h> |
7 | #if USE_SYS_RANDOM_H | |
8 | # include <sys/random.h> | |
9 | #endif | |
6e200d55 | 10 | #include <sys/stat.h> |
26ded557 | 11 | #include <sys/xattr.h> |
07630cea | 12 | #include <unistd.h> |
6e200d55 | 13 | |
8ba12aef LP |
14 | #include "sd-id128.h" |
15 | ||
b5efdb8a | 16 | #include "alloc-util.h" |
3ffd4af2 | 17 | #include "fd-util.h" |
4b3b5bc7 | 18 | #include "fs-util.h" |
c004493c | 19 | #include "io-util.h" |
6e200d55 | 20 | #include "log.h" |
5e332028 | 21 | #include "main-func.h" |
123aeae2 | 22 | #include "missing_random.h" |
f5947a5e | 23 | #include "missing_syscall.h" |
49e942b2 | 24 | #include "mkdir.h" |
26ded557 | 25 | #include "parse-util.h" |
3e155eba | 26 | #include "random-util.h" |
07630cea | 27 | #include "string-util.h" |
bf819d3a | 28 | #include "sync-util.h" |
da2862ef | 29 | #include "sha256.h" |
07630cea | 30 | #include "util.h" |
26ded557 LP |
31 | #include "xattr-util.h" |
32 | ||
33 | typedef enum CreditEntropy { | |
34 | CREDIT_ENTROPY_NO_WAY, | |
35 | CREDIT_ENTROPY_YES_PLEASE, | |
36 | CREDIT_ENTROPY_YES_FORCED, | |
37 | } CreditEntropy; | |
38 | ||
39 | static CreditEntropy may_credit(int seed_fd) { | |
40 | _cleanup_free_ char *creditable = NULL; | |
41 | const char *e; | |
42 | int r; | |
43 | ||
44 | assert(seed_fd >= 0); | |
45 | ||
46 | e = getenv("SYSTEMD_RANDOM_SEED_CREDIT"); | |
47 | if (!e) { | |
48 | log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is not set, not crediting entropy."); | |
49 | return CREDIT_ENTROPY_NO_WAY; | |
50 | } | |
51 | if (streq(e, "force")) { | |
52 | log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is set to 'force', crediting entropy."); | |
53 | return CREDIT_ENTROPY_YES_FORCED; | |
54 | } | |
55 | ||
56 | r = parse_boolean(e); | |
57 | if (r <= 0) { | |
58 | if (r < 0) | |
59 | log_warning_errno(r, "Failed to parse $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy: %m"); | |
60 | else | |
61 | log_debug("Crediting entropy is turned off via $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy."); | |
62 | ||
63 | return CREDIT_ENTROPY_NO_WAY; | |
64 | } | |
65 | ||
66 | /* Determine if the file is marked as creditable */ | |
67 | r = fgetxattr_malloc(seed_fd, "user.random-seed-creditable", &creditable); | |
68 | if (r < 0) { | |
00675c36 | 69 | if (ERRNO_IS_XATTR_ABSENT(r)) |
26ded557 LP |
70 | log_debug_errno(r, "Seed file is not marked as creditable, not crediting."); |
71 | else | |
72 | log_warning_errno(r, "Failed to read extended attribute, ignoring: %m"); | |
73 | ||
74 | return CREDIT_ENTROPY_NO_WAY; | |
75 | } | |
76 | ||
77 | r = parse_boolean(creditable); | |
78 | if (r <= 0) { | |
79 | if (r < 0) | |
80 | log_warning_errno(r, "Failed to parse user.random-seed-creditable extended attribute, ignoring: %s", creditable); | |
81 | else | |
82 | log_debug("Seed file is marked as not creditable, not crediting."); | |
83 | ||
84 | return CREDIT_ENTROPY_NO_WAY; | |
85 | } | |
86 | ||
87 | /* Don't credit the random seed if we are in first-boot mode, because we are supposed to start from | |
88 | * scratch. This is a safety precaution for cases where we people ship "golden" images with empty | |
89 | * /etc but populated /var that contains a random seed. */ | |
249d31b0 FB |
90 | r = RET_NERRNO(access("/run/systemd/first-boot", F_OK)); |
91 | if (r == -ENOENT) | |
92 | /* All is good, we are not in first-boot mode. */ | |
93 | return CREDIT_ENTROPY_YES_PLEASE; | |
94 | if (r < 0) { | |
95 | log_warning_errno(r, "Failed to check whether we are in first-boot mode, not crediting entropy: %m"); | |
26ded557 LP |
96 | return CREDIT_ENTROPY_NO_WAY; |
97 | } | |
98 | ||
249d31b0 FB |
99 | log_debug("Not crediting entropy, since booted in first-boot mode."); |
100 | return CREDIT_ENTROPY_NO_WAY; | |
26ded557 | 101 | } |
6e200d55 | 102 | |
72d0d7a6 | 103 | static int run(int argc, char *argv[]) { |
06511ba5 | 104 | bool read_seed_file, write_seed_file, synchronous, hashed_old_seed = false; |
ce179470 LP |
105 | _cleanup_close_ int seed_fd = -1, random_fd = -1; |
106 | _cleanup_free_ void* buf = NULL; | |
da2862ef | 107 | struct sha256_ctx hash_state; |
3e155eba | 108 | size_t buf_size; |
ac93390b | 109 | struct stat st; |
da2862ef | 110 | ssize_t k, l; |
ac93390b | 111 | int r; |
6e200d55 | 112 | |
d2acb93d | 113 | log_setup(); |
6e200d55 | 114 | |
baaa35ad ZJS |
115 | if (argc != 2) |
116 | return log_error_errno(SYNTHETIC_ERRNO(EINVAL), | |
117 | "This program requires one argument."); | |
72d0d7a6 | 118 | |
4c12626c LP |
119 | umask(0022); |
120 | ||
3e155eba | 121 | buf_size = random_pool_size(); |
26192dfc | 122 | |
5468d9af | 123 | r = mkdir_parents(RANDOM_SEED, 0755); |
72d0d7a6 ZJS |
124 | if (r < 0) |
125 | return log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m"); | |
b56e5747 | 126 | |
ac93390b LP |
127 | /* When we load the seed we read it and write it to the device and then immediately update the saved seed with |
128 | * new data, to make sure the next boot gets seeded differently. */ | |
6e200d55 LP |
129 | |
130 | if (streq(argv[1], "load")) { | |
131 | ||
ce179470 LP |
132 | seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
133 | if (seed_fd < 0) { | |
15d961bf LP |
134 | int open_rw_error = -errno; |
135 | ||
ac93390b | 136 | write_seed_file = false; |
8edc2d22 | 137 | |
ce179470 LP |
138 | seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY); |
139 | if (seed_fd < 0) { | |
8edc2d22 ZJS |
140 | bool missing = errno == ENOENT; |
141 | ||
142 | log_full_errno(missing ? LOG_DEBUG : LOG_ERR, | |
143 | open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m"); | |
144 | r = log_full_errno(missing ? LOG_DEBUG : LOG_ERR, | |
145 | errno, "Failed to open " RANDOM_SEED " for reading: %m"); | |
72d0d7a6 | 146 | return missing ? 0 : r; |
6e200d55 | 147 | } |
ac93390b LP |
148 | } else |
149 | write_seed_file = true; | |
6e200d55 | 150 | |
ce179470 | 151 | random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600); |
c6127c39 LP |
152 | if (random_fd < 0) |
153 | return log_error_errno(errno, "Failed to open /dev/urandom: %m"); | |
6e200d55 | 154 | |
ac93390b | 155 | read_seed_file = true; |
26ded557 | 156 | synchronous = true; /* make this invocation a synchronous barrier for random pool initialization */ |
6e200d55 LP |
157 | |
158 | } else if (streq(argv[1], "save")) { | |
159 | ||
ac93390b | 160 | random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); |
72d0d7a6 ZJS |
161 | if (random_fd < 0) |
162 | return log_error_errno(errno, "Failed to open /dev/urandom: %m"); | |
ac93390b | 163 | |
ce179470 | 164 | seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
72d0d7a6 ZJS |
165 | if (seed_fd < 0) |
166 | return log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m"); | |
6e200d55 | 167 | |
ac93390b LP |
168 | read_seed_file = false; |
169 | write_seed_file = true; | |
26ded557 | 170 | synchronous = false; |
baaa35ad ZJS |
171 | } else |
172 | return log_error_errno(SYNTHETIC_ERRNO(EINVAL), | |
173 | "Unknown verb '%s'.", argv[1]); | |
6e200d55 | 174 | |
72d0d7a6 ZJS |
175 | if (fstat(seed_fd, &st) < 0) |
176 | return log_error_errno(errno, "Failed to stat() seed file " RANDOM_SEED ": %m"); | |
ac93390b LP |
177 | |
178 | /* If the seed file is larger than what we expect, then honour the existing size and save/restore as much as it says */ | |
179 | if ((uint64_t) st.st_size > buf_size) | |
3e155eba | 180 | buf_size = MIN(st.st_size, RANDOM_POOL_SIZE_MAX); |
ac93390b LP |
181 | |
182 | buf = malloc(buf_size); | |
72d0d7a6 ZJS |
183 | if (!buf) |
184 | return log_oom(); | |
ac93390b LP |
185 | |
186 | if (read_seed_file) { | |
8ba12aef | 187 | sd_id128_t mid; |
26ded557 LP |
188 | |
189 | /* First, let's write the machine ID into /dev/urandom, not crediting entropy. Why? As an | |
190 | * extra protection against "golden images" that are put together sloppily, i.e. images which | |
191 | * are duplicated on multiple systems but where the random seed file is not properly | |
192 | * reset. Frequently the machine ID is properly reset on those systems however (simply | |
193 | * because it's easier to notice, if it isn't due to address clashes and so on, while random | |
194 | * seed equivalence is generally not noticed easily), hence let's simply write the machined | |
195 | * ID into the random pool too. */ | |
196 | r = sd_id128_get_machine(&mid); | |
197 | if (r < 0) | |
198 | log_debug_errno(r, "Failed to get machine ID, ignoring: %m"); | |
199 | else { | |
200 | r = loop_write(random_fd, &mid, sizeof(mid), false); | |
201 | if (r < 0) | |
202 | log_debug_errno(r, "Failed to write machine ID to /dev/urandom, ignoring: %m"); | |
203 | } | |
ac93390b LP |
204 | |
205 | k = loop_read(seed_fd, buf, buf_size, false); | |
206 | if (k < 0) | |
26ded557 LP |
207 | log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m"); |
208 | else if (k == 0) | |
ac93390b | 209 | log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding."); |
26ded557 LP |
210 | else { |
211 | CreditEntropy lets_credit; | |
212 | ||
06511ba5 JD |
213 | /* If we're going to later write out a seed file, initialize a hash state with |
214 | * the contents of the seed file we just read, so that the new one can't regress | |
215 | * in entropy. */ | |
216 | if (write_seed_file) { | |
217 | sha256_init_ctx(&hash_state); | |
218 | sha256_process_bytes(&k, sizeof(k), &hash_state); /* Hash length to distinguish from new seed. */ | |
219 | sha256_process_bytes(buf, k, &hash_state); | |
220 | hashed_old_seed = true; | |
221 | } | |
222 | ||
ac93390b LP |
223 | (void) lseek(seed_fd, 0, SEEK_SET); |
224 | ||
26ded557 | 225 | lets_credit = may_credit(seed_fd); |
8ba12aef | 226 | |
26ded557 LP |
227 | /* Before we credit or use the entropy, let's make sure to securely drop the |
228 | * creditable xattr from the file, so that we never credit the same random seed | |
229 | * again. Note that further down we'll write a new seed again, and likely mark it as | |
230 | * credible again, hence this is just paranoia to close the short time window between | |
231 | * the time we upload the random seed into the kernel and download the new one from | |
232 | * it. */ | |
233 | ||
234 | if (fremovexattr(seed_fd, "user.random-seed-creditable") < 0) { | |
00675c36 | 235 | if (!ERRNO_IS_XATTR_ABSENT(errno)) |
26ded557 LP |
236 | log_warning_errno(errno, "Failed to remove extended attribute, ignoring: %m"); |
237 | ||
238 | /* Otherwise, there was no creditable flag set, which is OK. */ | |
239 | } else { | |
240 | r = fsync_full(seed_fd); | |
241 | if (r < 0) { | |
242 | log_warning_errno(r, "Failed to synchronize seed to disk, not crediting entropy: %m"); | |
243 | ||
244 | if (lets_credit == CREDIT_ENTROPY_YES_PLEASE) | |
245 | lets_credit = CREDIT_ENTROPY_NO_WAY; | |
246 | } | |
247 | } | |
248 | ||
4dd055f9 LP |
249 | r = random_write_entropy(random_fd, buf, k, |
250 | IN_SET(lets_credit, CREDIT_ENTROPY_YES_PLEASE, CREDIT_ENTROPY_YES_FORCED)); | |
251 | if (r < 0) | |
252 | log_error_errno(r, "Failed to write seed to /dev/urandom: %m"); | |
8ba12aef | 253 | } |
ac93390b LP |
254 | } |
255 | ||
256 | if (write_seed_file) { | |
26ded557 | 257 | bool getrandom_worked = false; |
6e200d55 | 258 | |
26ded557 LP |
259 | /* This is just a safety measure. Given that we are root and most likely created the file |
260 | * ourselves the mode and owner should be correct anyway. */ | |
261 | r = fchmod_and_chown(seed_fd, 0600, 0, 0); | |
262 | if (r < 0) | |
e5b90b30 | 263 | return log_error_errno(r, "Failed to adjust seed file ownership and access mode: %m"); |
26ded557 LP |
264 | |
265 | /* Let's make this whole job asynchronous, i.e. let's make ourselves a barrier for | |
266 | * proper initialization of the random pool. */ | |
267 | k = getrandom(buf, buf_size, GRND_NONBLOCK); | |
268 | if (k < 0 && errno == EAGAIN && synchronous) { | |
269 | log_notice("Kernel entropy pool is not initialized yet, waiting until it is."); | |
270 | k = getrandom(buf, buf_size, 0); /* retry synchronously */ | |
271 | } | |
72d0d7a6 | 272 | if (k < 0) |
26ded557 LP |
273 | log_debug_errno(errno, "Failed to read random data with getrandom(), falling back to /dev/urandom: %m"); |
274 | else if ((size_t) k < buf_size) | |
111a3aae | 275 | log_debug("Short read from getrandom(), falling back to /dev/urandom."); |
26ded557 LP |
276 | else |
277 | getrandom_worked = true; | |
278 | ||
279 | if (!getrandom_worked) { | |
280 | /* Retry with classic /dev/urandom */ | |
281 | k = loop_read(random_fd, buf, buf_size, false); | |
282 | if (k < 0) | |
283 | return log_error_errno(k, "Failed to read new seed from /dev/urandom: %m"); | |
284 | if (k == 0) | |
285 | return log_error_errno(SYNTHETIC_ERRNO(EIO), | |
286 | "Got EOF while reading from /dev/urandom."); | |
287 | } | |
1509fb87 | 288 | |
da2862ef JD |
289 | /* If we previously read in a seed file, then hash the new seed into the old one, |
290 | * and replace the last 32 bytes of the seed with the hash output, so that the | |
291 | * new seed file can't regress in entropy. */ | |
06511ba5 | 292 | if (hashed_old_seed) { |
00b46638 | 293 | uint8_t hash[SHA256_DIGEST_SIZE]; |
06511ba5 | 294 | sha256_process_bytes(&k, sizeof(k), &hash_state); /* Hash length to distinguish from old seed. */ |
da2862ef JD |
295 | sha256_process_bytes(buf, k, &hash_state); |
296 | sha256_finish_ctx(&hash_state, hash); | |
06511ba5 | 297 | l = MIN((size_t)k, sizeof(hash)); |
da2862ef JD |
298 | memcpy((uint8_t *)buf + k - l, hash, l); |
299 | } | |
300 | ||
1509fb87 LP |
301 | r = loop_write(seed_fd, buf, (size_t) k, false); |
302 | if (r < 0) | |
72d0d7a6 | 303 | return log_error_errno(r, "Failed to write new random seed file: %m"); |
26ded557 LP |
304 | |
305 | if (ftruncate(seed_fd, k) < 0) | |
306 | return log_error_errno(r, "Failed to truncate random seed file: %m"); | |
307 | ||
308 | r = fsync_full(seed_fd); | |
309 | if (r < 0) | |
310 | return log_error_errno(r, "Failed to synchronize seed file: %m"); | |
311 | ||
312 | /* If we got this random seed data from getrandom() the data is suitable for crediting | |
313 | * entropy later on. Let's keep that in mind by setting an extended attribute. on the file */ | |
314 | if (getrandom_worked) | |
315 | if (fsetxattr(seed_fd, "user.random-seed-creditable", "1", 1, 0) < 0) | |
97f1c6af | 316 | log_full_errno(ERRNO_IS_NOT_SUPPORTED(errno) ? LOG_DEBUG : LOG_WARNING, errno, |
26ded557 | 317 | "Failed to mark seed file as creditable, ignoring: %m"); |
6e200d55 LP |
318 | } |
319 | ||
26ded557 | 320 | return 0; |
6e200d55 | 321 | } |
72d0d7a6 ZJS |
322 | |
323 | DEFINE_MAIN_FUNCTION(run); |