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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) { | |
69 | if (IN_SET(r, -ENODATA, -ENOSYS, -EOPNOTSUPP)) | |
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. */ | |
90 | if (access("/run/systemd/first-boot", F_OK) < 0) { | |
91 | ||
92 | if (errno != ENOENT) { | |
93 | log_warning_errno(errno, "Failed to check whether we are in first-boot mode, not crediting entropy: %m"); | |
94 | return CREDIT_ENTROPY_NO_WAY; | |
95 | } | |
96 | ||
97 | /* If ENOENT all is good, we are not in first-boot mode. */ | |
98 | } else { | |
99 | log_debug("Not crediting entropy, since booted in first-boot mode."); | |
100 | return CREDIT_ENTROPY_NO_WAY; | |
101 | } | |
102 | ||
103 | return CREDIT_ENTROPY_YES_PLEASE; | |
104 | } | |
6e200d55 | 105 | |
72d0d7a6 | 106 | static int run(int argc, char *argv[]) { |
06511ba5 | 107 | bool read_seed_file, write_seed_file, synchronous, hashed_old_seed = false; |
ce179470 LP |
108 | _cleanup_close_ int seed_fd = -1, random_fd = -1; |
109 | _cleanup_free_ void* buf = NULL; | |
da2862ef | 110 | struct sha256_ctx hash_state; |
3e155eba | 111 | size_t buf_size; |
ac93390b | 112 | struct stat st; |
da2862ef | 113 | ssize_t k, l; |
ac93390b | 114 | int r; |
6e200d55 | 115 | |
d2acb93d | 116 | log_setup(); |
6e200d55 | 117 | |
baaa35ad ZJS |
118 | if (argc != 2) |
119 | return log_error_errno(SYNTHETIC_ERRNO(EINVAL), | |
120 | "This program requires one argument."); | |
72d0d7a6 | 121 | |
4c12626c LP |
122 | umask(0022); |
123 | ||
3e155eba | 124 | buf_size = random_pool_size(); |
26192dfc | 125 | |
5468d9af | 126 | r = mkdir_parents(RANDOM_SEED, 0755); |
72d0d7a6 ZJS |
127 | if (r < 0) |
128 | return log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m"); | |
b56e5747 | 129 | |
ac93390b LP |
130 | /* When we load the seed we read it and write it to the device and then immediately update the saved seed with |
131 | * new data, to make sure the next boot gets seeded differently. */ | |
6e200d55 LP |
132 | |
133 | if (streq(argv[1], "load")) { | |
134 | ||
ce179470 LP |
135 | seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
136 | if (seed_fd < 0) { | |
15d961bf LP |
137 | int open_rw_error = -errno; |
138 | ||
ac93390b | 139 | write_seed_file = false; |
8edc2d22 | 140 | |
ce179470 LP |
141 | seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY); |
142 | if (seed_fd < 0) { | |
8edc2d22 ZJS |
143 | bool missing = errno == ENOENT; |
144 | ||
145 | log_full_errno(missing ? LOG_DEBUG : LOG_ERR, | |
146 | open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m"); | |
147 | r = log_full_errno(missing ? LOG_DEBUG : LOG_ERR, | |
148 | errno, "Failed to open " RANDOM_SEED " for reading: %m"); | |
72d0d7a6 | 149 | return missing ? 0 : r; |
6e200d55 | 150 | } |
ac93390b LP |
151 | } else |
152 | write_seed_file = true; | |
6e200d55 | 153 | |
ce179470 | 154 | random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600); |
c6127c39 LP |
155 | if (random_fd < 0) |
156 | return log_error_errno(errno, "Failed to open /dev/urandom: %m"); | |
6e200d55 | 157 | |
ac93390b | 158 | read_seed_file = true; |
26ded557 | 159 | synchronous = true; /* make this invocation a synchronous barrier for random pool initialization */ |
6e200d55 LP |
160 | |
161 | } else if (streq(argv[1], "save")) { | |
162 | ||
ac93390b | 163 | random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); |
72d0d7a6 ZJS |
164 | if (random_fd < 0) |
165 | return log_error_errno(errno, "Failed to open /dev/urandom: %m"); | |
ac93390b | 166 | |
ce179470 | 167 | seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
72d0d7a6 ZJS |
168 | if (seed_fd < 0) |
169 | return log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m"); | |
6e200d55 | 170 | |
ac93390b LP |
171 | read_seed_file = false; |
172 | write_seed_file = true; | |
26ded557 | 173 | synchronous = false; |
baaa35ad ZJS |
174 | } else |
175 | return log_error_errno(SYNTHETIC_ERRNO(EINVAL), | |
176 | "Unknown verb '%s'.", argv[1]); | |
6e200d55 | 177 | |
72d0d7a6 ZJS |
178 | if (fstat(seed_fd, &st) < 0) |
179 | return log_error_errno(errno, "Failed to stat() seed file " RANDOM_SEED ": %m"); | |
ac93390b LP |
180 | |
181 | /* If the seed file is larger than what we expect, then honour the existing size and save/restore as much as it says */ | |
182 | if ((uint64_t) st.st_size > buf_size) | |
3e155eba | 183 | buf_size = MIN(st.st_size, RANDOM_POOL_SIZE_MAX); |
ac93390b LP |
184 | |
185 | buf = malloc(buf_size); | |
72d0d7a6 ZJS |
186 | if (!buf) |
187 | return log_oom(); | |
ac93390b LP |
188 | |
189 | if (read_seed_file) { | |
8ba12aef | 190 | sd_id128_t mid; |
26ded557 LP |
191 | |
192 | /* First, let's write the machine ID into /dev/urandom, not crediting entropy. Why? As an | |
193 | * extra protection against "golden images" that are put together sloppily, i.e. images which | |
194 | * are duplicated on multiple systems but where the random seed file is not properly | |
195 | * reset. Frequently the machine ID is properly reset on those systems however (simply | |
196 | * because it's easier to notice, if it isn't due to address clashes and so on, while random | |
197 | * seed equivalence is generally not noticed easily), hence let's simply write the machined | |
198 | * ID into the random pool too. */ | |
199 | r = sd_id128_get_machine(&mid); | |
200 | if (r < 0) | |
201 | log_debug_errno(r, "Failed to get machine ID, ignoring: %m"); | |
202 | else { | |
203 | r = loop_write(random_fd, &mid, sizeof(mid), false); | |
204 | if (r < 0) | |
205 | log_debug_errno(r, "Failed to write machine ID to /dev/urandom, ignoring: %m"); | |
206 | } | |
ac93390b LP |
207 | |
208 | k = loop_read(seed_fd, buf, buf_size, false); | |
209 | if (k < 0) | |
26ded557 LP |
210 | log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m"); |
211 | else if (k == 0) | |
ac93390b | 212 | log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding."); |
26ded557 LP |
213 | else { |
214 | CreditEntropy lets_credit; | |
215 | ||
06511ba5 JD |
216 | /* If we're going to later write out a seed file, initialize a hash state with |
217 | * the contents of the seed file we just read, so that the new one can't regress | |
218 | * in entropy. */ | |
219 | if (write_seed_file) { | |
220 | sha256_init_ctx(&hash_state); | |
221 | sha256_process_bytes(&k, sizeof(k), &hash_state); /* Hash length to distinguish from new seed. */ | |
222 | sha256_process_bytes(buf, k, &hash_state); | |
223 | hashed_old_seed = true; | |
224 | } | |
225 | ||
ac93390b LP |
226 | (void) lseek(seed_fd, 0, SEEK_SET); |
227 | ||
26ded557 | 228 | lets_credit = may_credit(seed_fd); |
8ba12aef | 229 | |
26ded557 LP |
230 | /* Before we credit or use the entropy, let's make sure to securely drop the |
231 | * creditable xattr from the file, so that we never credit the same random seed | |
232 | * again. Note that further down we'll write a new seed again, and likely mark it as | |
233 | * credible again, hence this is just paranoia to close the short time window between | |
234 | * the time we upload the random seed into the kernel and download the new one from | |
235 | * it. */ | |
236 | ||
237 | if (fremovexattr(seed_fd, "user.random-seed-creditable") < 0) { | |
238 | if (!IN_SET(errno, ENODATA, ENOSYS, EOPNOTSUPP)) | |
239 | log_warning_errno(errno, "Failed to remove extended attribute, ignoring: %m"); | |
240 | ||
241 | /* Otherwise, there was no creditable flag set, which is OK. */ | |
242 | } else { | |
243 | r = fsync_full(seed_fd); | |
244 | if (r < 0) { | |
245 | log_warning_errno(r, "Failed to synchronize seed to disk, not crediting entropy: %m"); | |
246 | ||
247 | if (lets_credit == CREDIT_ENTROPY_YES_PLEASE) | |
248 | lets_credit = CREDIT_ENTROPY_NO_WAY; | |
249 | } | |
250 | } | |
251 | ||
4dd055f9 LP |
252 | r = random_write_entropy(random_fd, buf, k, |
253 | IN_SET(lets_credit, CREDIT_ENTROPY_YES_PLEASE, CREDIT_ENTROPY_YES_FORCED)); | |
254 | if (r < 0) | |
255 | log_error_errno(r, "Failed to write seed to /dev/urandom: %m"); | |
8ba12aef | 256 | } |
ac93390b LP |
257 | } |
258 | ||
259 | if (write_seed_file) { | |
26ded557 | 260 | bool getrandom_worked = false; |
6e200d55 | 261 | |
26ded557 LP |
262 | /* This is just a safety measure. Given that we are root and most likely created the file |
263 | * ourselves the mode and owner should be correct anyway. */ | |
264 | r = fchmod_and_chown(seed_fd, 0600, 0, 0); | |
265 | if (r < 0) | |
e5b90b30 | 266 | return log_error_errno(r, "Failed to adjust seed file ownership and access mode: %m"); |
26ded557 LP |
267 | |
268 | /* Let's make this whole job asynchronous, i.e. let's make ourselves a barrier for | |
269 | * proper initialization of the random pool. */ | |
270 | k = getrandom(buf, buf_size, GRND_NONBLOCK); | |
271 | if (k < 0 && errno == EAGAIN && synchronous) { | |
272 | log_notice("Kernel entropy pool is not initialized yet, waiting until it is."); | |
273 | k = getrandom(buf, buf_size, 0); /* retry synchronously */ | |
274 | } | |
72d0d7a6 | 275 | if (k < 0) |
26ded557 LP |
276 | log_debug_errno(errno, "Failed to read random data with getrandom(), falling back to /dev/urandom: %m"); |
277 | else if ((size_t) k < buf_size) | |
111a3aae | 278 | log_debug("Short read from getrandom(), falling back to /dev/urandom."); |
26ded557 LP |
279 | else |
280 | getrandom_worked = true; | |
281 | ||
282 | if (!getrandom_worked) { | |
283 | /* Retry with classic /dev/urandom */ | |
284 | k = loop_read(random_fd, buf, buf_size, false); | |
285 | if (k < 0) | |
286 | return log_error_errno(k, "Failed to read new seed from /dev/urandom: %m"); | |
287 | if (k == 0) | |
288 | return log_error_errno(SYNTHETIC_ERRNO(EIO), | |
289 | "Got EOF while reading from /dev/urandom."); | |
290 | } | |
1509fb87 | 291 | |
da2862ef JD |
292 | /* If we previously read in a seed file, then hash the new seed into the old one, |
293 | * and replace the last 32 bytes of the seed with the hash output, so that the | |
294 | * new seed file can't regress in entropy. */ | |
06511ba5 JD |
295 | if (hashed_old_seed) { |
296 | uint8_t hash[32]; | |
297 | sha256_process_bytes(&k, sizeof(k), &hash_state); /* Hash length to distinguish from old seed. */ | |
da2862ef JD |
298 | sha256_process_bytes(buf, k, &hash_state); |
299 | sha256_finish_ctx(&hash_state, hash); | |
06511ba5 | 300 | l = MIN((size_t)k, sizeof(hash)); |
da2862ef JD |
301 | memcpy((uint8_t *)buf + k - l, hash, l); |
302 | } | |
303 | ||
1509fb87 LP |
304 | r = loop_write(seed_fd, buf, (size_t) k, false); |
305 | if (r < 0) | |
72d0d7a6 | 306 | return log_error_errno(r, "Failed to write new random seed file: %m"); |
26ded557 LP |
307 | |
308 | if (ftruncate(seed_fd, k) < 0) | |
309 | return log_error_errno(r, "Failed to truncate random seed file: %m"); | |
310 | ||
311 | r = fsync_full(seed_fd); | |
312 | if (r < 0) | |
313 | return log_error_errno(r, "Failed to synchronize seed file: %m"); | |
314 | ||
315 | /* If we got this random seed data from getrandom() the data is suitable for crediting | |
316 | * entropy later on. Let's keep that in mind by setting an extended attribute. on the file */ | |
317 | if (getrandom_worked) | |
318 | if (fsetxattr(seed_fd, "user.random-seed-creditable", "1", 1, 0) < 0) | |
97f1c6af | 319 | log_full_errno(ERRNO_IS_NOT_SUPPORTED(errno) ? LOG_DEBUG : LOG_WARNING, errno, |
26ded557 | 320 | "Failed to mark seed file as creditable, ignoring: %m"); |
6e200d55 LP |
321 | } |
322 | ||
26ded557 | 323 | return 0; |
6e200d55 | 324 | } |
72d0d7a6 ZJS |
325 | |
326 | DEFINE_MAIN_FUNCTION(run); |