package/system/urandom-seed/seedrng.c

   1 // SPDX-License-Identifier: (GPL-2.0 OR MIT OR Apache-2.0)
   2 /*
   3  * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
   4  */
   5
   6 #include <linux/random.h>
   7 #include <sys/random.h>
   8 #include <sys/ioctl.h>
   9 #include <sys/file.h>
  10 #include <sys/stat.h>
  11 #include <sys/types.h>
  12 #include <fcntl.h>
  13 #include <poll.h>
  14 #include <unistd.h>
  15 #include <time.h>
  16 #include <errno.h>
  17 #include <endian.h>
  18 #include <stdbool.h>
  19 #include <stdint.h>
  20 #include <string.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23
  24 #define SEED_DIR "/etc/seedrng"
  25 #define CREDITABLE_SEED SEED_DIR "/seed.credit"
  26 #define NON_CREDITABLE_SEED SEED_DIR "/seed.no-credit"
  27 #define LOCK_FILE "/tmp/run/seedrng.lock"
  28
  29 enum blake2s_lengths {
  30         BLAKE2S_BLOCK_LEN = 64,
  31         BLAKE2S_HASH_LEN = 32,
  32         BLAKE2S_KEY_LEN = 32
  33 };
  34
  35 enum seedrng_lengths {
  36         MAX_SEED_LEN = 512,
  37         MIN_SEED_LEN = BLAKE2S_HASH_LEN
  38 };
  39
  40 struct blake2s_state {
  41         uint32_t h[8];
  42         uint32_t t[2];
  43         uint32_t f[2];
  44         uint8_t buf[BLAKE2S_BLOCK_LEN];
  45         unsigned int buflen;
  46         unsigned int outlen;
  47 };
  48
  49 #define le32_to_cpup(a) le32toh(*(a))
  50 #define cpu_to_le32(a) htole32(a)
  51 #ifndef ARRAY_SIZE
  52 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
  53 #endif
  54 #ifndef DIV_ROUND_UP
  55 #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
  56 #endif
  57
  58 static inline void cpu_to_le32_array(uint32_t *buf, unsigned int words)
  59 {
  60         while (words--) {
  61                 *buf = cpu_to_le32(*buf);
  62                 ++buf;
  63         }
  64 }
  65
  66 static inline void le32_to_cpu_array(uint32_t *buf, unsigned int words)
  67 {
  68         while (words--) {
  69                 *buf = le32_to_cpup(buf);
  70                 ++buf;
  71         }
  72 }
  73
  74 static inline uint32_t ror32(uint32_t word, unsigned int shift)
  75 {
  76         return (word >> (shift & 31)) | (word << ((-shift) & 31));
  77 }
  78
  79 static const uint32_t blake2s_iv[8] = {
  80         0x6A09E667UL, 0xBB67AE85UL, 0x3C6EF372UL, 0xA54FF53AUL,
  81         0x510E527FUL, 0x9B05688CUL, 0x1F83D9ABUL, 0x5BE0CD19UL
  82 };
  83
  84 static const uint8_t blake2s_sigma[10][16] = {
  85         { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
  86         { 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 },
  87         { 11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4 },
  88         { 7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8 },
  89         { 9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13 },
  90         { 2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9 },
  91         { 12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11 },
  92         { 13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10 },
  93         { 6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5 },
  94         { 10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0 },
  95 };
  96
  97 static void blake2s_set_lastblock(struct blake2s_state *state)
  98 {
  99         state->f[0] = -1;
 100 }
 101
 102 static void blake2s_increment_counter(struct blake2s_state *state, const uint32_t inc)
 103 {
 104         state->t[0] += inc;
 105         state->t[1] += (state->t[0] < inc);
 106 }
 107
 108 static void blake2s_init_param(struct blake2s_state *state, const uint32_t param)
 109 {
 110         int i;
 111
 112         memset(state, 0, sizeof(*state));
 113         for (i = 0; i < 8; ++i)
 114                 state->h[i] = blake2s_iv[i];
 115         state->h[0] ^= param;
 116 }
 117
 118 static void blake2s_init(struct blake2s_state *state, const size_t outlen)
 119 {
 120         blake2s_init_param(state, 0x01010000 | outlen);
 121         state->outlen = outlen;
 122 }
 123
 124 static void blake2s_compress(struct blake2s_state *state, const uint8_t *block, size_t nblocks, const uint32_t inc)
 125 {
 126         uint32_t m[16];
 127         uint32_t v[16];
 128         int i;
 129
 130         while (nblocks > 0) {
 131                 blake2s_increment_counter(state, inc);
 132                 memcpy(m, block, BLAKE2S_BLOCK_LEN);
 133                 le32_to_cpu_array(m, ARRAY_SIZE(m));
 134                 memcpy(v, state->h, 32);
 135                 v[ 8] = blake2s_iv[0];
 136                 v[ 9] = blake2s_iv[1];
 137                 v[10] = blake2s_iv[2];
 138                 v[11] = blake2s_iv[3];
 139                 v[12] = blake2s_iv[4] ^ state->t[0];
 140                 v[13] = blake2s_iv[5] ^ state->t[1];
 141                 v[14] = blake2s_iv[6] ^ state->f[0];
 142                 v[15] = blake2s_iv[7] ^ state->f[1];
 143
 144 #define G(r, i, a, b, c, d) do { \
 145         a += b + m[blake2s_sigma[r][2 * i + 0]]; \
 146         d = ror32(d ^ a, 16); \
 147         c += d; \
 148         b = ror32(b ^ c, 12); \
 149         a += b + m[blake2s_sigma[r][2 * i + 1]]; \
 150         d = ror32(d ^ a, 8); \
 151         c += d; \
 152         b = ror32(b ^ c, 7); \
 153 } while (0)
 154
 155 #define ROUND(r) do { \
 156         G(r, 0, v[0], v[ 4], v[ 8], v[12]); \
 157         G(r, 1, v[1], v[ 5], v[ 9], v[13]); \
 158         G(r, 2, v[2], v[ 6], v[10], v[14]); \
 159         G(r, 3, v[3], v[ 7], v[11], v[15]); \
 160         G(r, 4, v[0], v[ 5], v[10], v[15]); \
 161         G(r, 5, v[1], v[ 6], v[11], v[12]); \
 162         G(r, 6, v[2], v[ 7], v[ 8], v[13]); \
 163         G(r, 7, v[3], v[ 4], v[ 9], v[14]); \
 164 } while (0)
 165                 ROUND(0);
 166                 ROUND(1);
 167                 ROUND(2);
 168                 ROUND(3);
 169                 ROUND(4);
 170                 ROUND(5);
 171                 ROUND(6);
 172                 ROUND(7);
 173                 ROUND(8);
 174                 ROUND(9);
 175
 176 #undef G
 177 #undef ROUND
 178
 179                 for (i = 0; i < 8; ++i)
 180                         state->h[i] ^= v[i] ^ v[i + 8];
 181
 182                 block += BLAKE2S_BLOCK_LEN;
 183                 --nblocks;
 184         }
 185 }
 186
 187 static void blake2s_update(struct blake2s_state *state, const void *inp, size_t inlen)
 188 {
 189         const size_t fill = BLAKE2S_BLOCK_LEN - state->buflen;
 190         const uint8_t *in = inp;
 191
 192         if (!inlen)
 193                 return;
 194         if (inlen > fill) {
 195                 memcpy(state->buf + state->buflen, in, fill);
 196                 blake2s_compress(state, state->buf, 1, BLAKE2S_BLOCK_LEN);
 197                 state->buflen = 0;
 198                 in += fill;
 199                 inlen -= fill;
 200         }
 201         if (inlen > BLAKE2S_BLOCK_LEN) {
 202                 const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_LEN);
 203                 blake2s_compress(state, in, nblocks - 1, BLAKE2S_BLOCK_LEN);
 204                 in += BLAKE2S_BLOCK_LEN * (nblocks - 1);
 205                 inlen -= BLAKE2S_BLOCK_LEN * (nblocks - 1);
 206         }
 207         memcpy(state->buf + state->buflen, in, inlen);
 208         state->buflen += inlen;
 209 }
 210
 211 static void blake2s_final(struct blake2s_state *state, uint8_t *out)
 212 {
 213         blake2s_set_lastblock(state);
 214         memset(state->buf + state->buflen, 0, BLAKE2S_BLOCK_LEN - state->buflen);
 215         blake2s_compress(state, state->buf, 1, state->buflen);
 216         cpu_to_le32_array(state->h, ARRAY_SIZE(state->h));
 217         memcpy(out, state->h, state->outlen);
 218 }
 219
 220 static size_t determine_optimal_seed_len(void)
 221 {
 222         size_t ret = 0;
 223         char poolsize_str[11] = { 0 };
 224         int fd = open("/proc/sys/kernel/random/poolsize", O_RDONLY);
 225
 226         if (fd < 0 || read(fd, poolsize_str, sizeof(poolsize_str) - 1) < 0) {
 227                 fprintf(stderr, "WARNING: Unable to determine pool size, falling back to %u bits: %s\n", MIN_SEED_LEN * 8, strerror(errno));
 228                 ret = MIN_SEED_LEN;
 229         } else
 230                 ret = DIV_ROUND_UP(strtoul(poolsize_str, NULL, 10), 8);
 231         if (fd >= 0)
 232                 close(fd);
 233         if (ret < MIN_SEED_LEN)
 234                 ret = MIN_SEED_LEN;
 235         else if (ret > MAX_SEED_LEN)
 236                 ret = MAX_SEED_LEN;
 237         return ret;
 238 }
 239
 240 static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable)
 241 {
 242         ssize_t ret;
 243         int urandom_fd;
 244
 245         *is_creditable = false;
 246         ret = getrandom(seed, len, GRND_NONBLOCK);
 247         if (ret == (ssize_t)len) {
 248                 *is_creditable = true;
 249                 return 0;
 250         } else if (ret < 0 && errno == ENOSYS) {
 251                 struct pollfd random_fd = {
 252                         .fd = open("/dev/random", O_RDONLY),
 253                         .events = POLLIN
 254                 };
 255                 if (random_fd.fd < 0)
 256                         return -errno;
 257                 *is_creditable = poll(&random_fd, 1, 0) == 1;
 258                 close(random_fd.fd);
 259         } else if (getrandom(seed, len, GRND_INSECURE) == (ssize_t)len)
 260                 return 0;
 261         urandom_fd = open("/dev/urandom", O_RDONLY);
 262         if (urandom_fd < 0)
 263                 return -errno;
 264         ret = read(urandom_fd, seed, len);
 265         if (ret == (ssize_t)len)
 266                 ret = 0;
 267         else
 268                 ret = -errno ? -errno : -EIO;
 269         close(urandom_fd);
 270         return ret;
 271 }
 272
 273 static int seed_rng(uint8_t *seed, size_t len, bool credit)
 274 {
 275         struct {
 276                 int entropy_count;
 277                 int buf_size;
 278                 uint8_t buffer[MAX_SEED_LEN];
 279         } req = {
 280                 .entropy_count = credit ? len * 8 : 0,
 281                 .buf_size = len
 282         };
 283         int random_fd, ret;
 284
 285         if (len > sizeof(req.buffer))
 286                 return -EFBIG;
 287         memcpy(req.buffer, seed, len);
 288
 289         random_fd = open("/dev/random", O_RDWR);
 290         if (random_fd < 0)
 291                 return -errno;
 292         ret = ioctl(random_fd, RNDADDENTROPY, &req);
 293         if (ret)
 294                 ret = -errno ? -errno : -EIO;
 295         close(random_fd);
 296         return ret;
 297 }
 298
 299 static int seed_from_file_if_exists(const char *filename, bool credit, struct blake2s_state *hash)
 300 {
 301         uint8_t seed[MAX_SEED_LEN];
 302         ssize_t seed_len;
 303         int fd, dfd, ret = 0;
 304
 305         fd = open(filename, O_RDONLY);
 306         if (fd < 0 && errno == ENOENT)
 307                 return 0;
 308         else if (fd < 0) {
 309                 ret = -errno;
 310                 fprintf(stderr, "ERROR: Unable to open seed file: %s\n", strerror(errno));
 311                 return ret;
 312         }
 313         dfd = open(SEED_DIR, O_DIRECTORY | O_RDONLY);
 314         if (dfd < 0) {
 315                 ret = -errno;
 316                 close(fd);
 317                 fprintf(stderr, "ERROR: Unable to open seed directory: %s\n", strerror(errno));
 318                 return ret;
 319         }
 320         seed_len = read(fd, seed, sizeof(seed));
 321         if (seed_len < 0) {
 322                 ret = -errno;
 323                 fprintf(stderr, "ERROR: Unable to read seed file: %s\n", strerror(errno));
 324         }
 325         close(fd);
 326         if (ret) {
 327                 close(dfd);
 328                 return ret;
 329         }
 330         if ((unlink(filename) < 0 || fsync(dfd) < 0) && seed_len) {
 331                 ret = -errno;
 332                 fprintf(stderr, "ERROR: Unable to remove seed after reading, so not seeding: %s\n", strerror(errno));
 333         }
 334         close(dfd);
 335         if (ret)
 336                 return ret;
 337         if (!seed_len)
 338                 return 0;
 339
 340         blake2s_update(hash, &seed_len, sizeof(seed_len));
 341         blake2s_update(hash, seed, seed_len);
 342
 343         fprintf(stdout, "Seeding %zd bits %s crediting\n", seed_len * 8, credit ? "and" : "without");
 344         ret = seed_rng(seed, seed_len, credit);
 345         if (ret < 0)
 346                 fprintf(stderr, "ERROR: Unable to seed: %s\n", strerror(-ret));
 347         return ret;
 348 }
 349
 350 static bool skip_credit(void)
 351 {
 352         const char *skip = getenv("SEEDRNG_SKIP_CREDIT");
 353         return skip && (!strcmp(skip, "1") || !strcasecmp(skip, "true") ||
 354                         !strcasecmp(skip, "yes") || !strcasecmp(skip, "y"));
 355 }
 356
 357 int main(int argc __attribute__((unused)), char *argv[] __attribute__((unused)))
 358 {
 359         static const char seedrng_prefix[] = "SeedRNG v1 Old+New Prefix";
 360         static const char seedrng_failure[] = "SeedRNG v1 No New Seed Failure";
 361         int ret, fd = -1, lock, program_ret = 0;
 362         uint8_t new_seed[MAX_SEED_LEN];
 363         size_t new_seed_len;
 364         bool new_seed_creditable;
 365         struct timespec realtime = { 0 }, boottime = { 0 };
 366         struct blake2s_state hash;
 367
 368         umask(0077);
 369         if (getuid()) {
 370                 fprintf(stderr, "ERROR: This program requires root\n");
 371                 return 1;
 372         }
 373
 374         blake2s_init(&hash, BLAKE2S_HASH_LEN);
 375         blake2s_update(&hash, seedrng_prefix, strlen(seedrng_prefix));
 376         clock_gettime(CLOCK_REALTIME, &realtime);
 377         clock_gettime(CLOCK_BOOTTIME, &boottime);
 378         blake2s_update(&hash, &realtime, sizeof(realtime));
 379         blake2s_update(&hash, &boottime, sizeof(boottime));
 380
 381         if (mkdir(SEED_DIR, 0700) < 0 && errno != EEXIST) {
 382                 fprintf(stderr, "ERROR: Unable to create \"%s\" directory: %s\n", SEED_DIR, strerror(errno));
 383                 return 1;
 384         }
 385
 386         lock = open(LOCK_FILE, O_WRONLY | O_CREAT, 0000);
 387         if (lock < 0 || flock(lock, LOCK_EX) < 0) {
 388                 fprintf(stderr, "ERROR: Unable to open lock file: %s\n", strerror(errno));
 389                 program_ret = 1;
 390                 goto out;
 391         }
 392
 393         ret = seed_from_file_if_exists(NON_CREDITABLE_SEED, false, &hash);
 394         if (ret < 0)
 395                 program_ret |= 1 << 1;
 396         ret = seed_from_file_if_exists(CREDITABLE_SEED, !skip_credit(), &hash);
 397         if (ret < 0)
 398                 program_ret |= 1 << 2;
 399
 400         new_seed_len = determine_optimal_seed_len();
 401         ret = read_new_seed(new_seed, new_seed_len, &new_seed_creditable);
 402         if (ret < 0) {
 403                 fprintf(stderr, "ERROR: Unable to read new seed: %s\n", strerror(-ret));
 404                 new_seed_len = BLAKE2S_HASH_LEN;
 405                 strncpy((char *)new_seed, seedrng_failure, new_seed_len);
 406                 program_ret |= 1 << 3;
 407         }
 408         blake2s_update(&hash, &new_seed_len, sizeof(new_seed_len));
 409         blake2s_update(&hash, new_seed, new_seed_len);
 410         blake2s_final(&hash, new_seed + new_seed_len - BLAKE2S_HASH_LEN);
 411
 412         fprintf(stdout, "Saving %zu bits of %s seed for next boot\n", new_seed_len * 8, new_seed_creditable ? "creditable" : "non-creditable");
 413         fd = open(NON_CREDITABLE_SEED, O_WRONLY | O_CREAT | O_TRUNC, 0400);
 414         if (fd < 0) {
 415                 fprintf(stderr, "ERROR: Unable to open seed file for writing: %s\n", strerror(errno));
 416                 program_ret |= 1 << 4;
 417                 goto out;
 418         }
 419         if (write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
 420                 fprintf(stderr, "ERROR: Unable to write seed file: %s\n", strerror(errno));
 421                 program_ret |= 1 << 5;
 422                 goto out;
 423         }
 424         if (new_seed_creditable && rename(NON_CREDITABLE_SEED, CREDITABLE_SEED) < 0) {
 425                 fprintf(stderr, "WARNING: Unable to make new seed creditable: %s\n", strerror(errno));
 426                 program_ret |= 1 << 6;
 427         }
 428 out:
 429         if (fd >= 0)
 430                 close(fd);
 431         if (lock >= 0)
 432                 close(lock);
 433         return program_ret;
 434 }