52f3cf7e5
Denys Vlasenko
2022-04-30
Subject
seedrng: simplify read_new_seed() to not have error return
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util-linux/seedrng.c+17 -14
| @@ -75,31 +75,38 @@ static size_t determine_optimal_seed_len(void) | |
| return MAX(MIN(poolsize, MAX_SEED_LEN), MIN_SEED_LEN); | |
| } | |
| - | static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable) |
| + | static bool read_new_seed(uint8_t *seed, size_t len) |
| { | |
| + | bool is_creditable; |
| ssize_t ret; | |
| ret = getrandom(seed, len, GRND_NONBLOCK); | |
| if (ret == (ssize_t)len) { | |
| - | *is_creditable = true; |
| - | return 0; |
| + | return true; |
| } | |
| if (ret < 0 && errno == ENOSYS) { | |
| struct pollfd random_fd = { | |
| .fd = xopen("/dev/random", O_RDONLY), | |
| .events = POLLIN | |
| }; | |
| - | *is_creditable = poll(&random_fd, 1, 0) == 1; |
| + | is_creditable = poll(&random_fd, 1, 0) == 1; |
| + | //This is racy. is_creditable can be set to true here, but other process |
| + | //can consume "good" random data from /dev/urandom before we do it below. |
| close(random_fd.fd); | |
| } else { | |
| - | *is_creditable = false; |
| if (getrandom(seed, len, GRND_INSECURE) == (ssize_t)len) | |
| - | return 0; |
| + | return false; |
| + | is_creditable = false; |
| } | |
| + | |
| + | /* Either getrandom() is not implemented, or |
| + | * getrandom(GRND_INSECURE) did not give us LEN bytes. |
| + | * Fallback to reading /dev/urandom. |
| + | */ |
| errno = 0; | |
| if (open_read_close("/dev/urandom", seed, len) != (ssize_t)len) | |
| bb_perror_msg_and_die("can't read '%s'", "/dev/urandom"); | |
| - | return 0; |
| + | return is_creditable; |
| } | |
| static void seed_rng(uint8_t *seed, size_t len, bool credit) | |
| @@ -190,17 +197,13 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) | |
| } | |
| new_seed_len = determine_optimal_seed_len(); | |
| - | if (read_new_seed(new_seed, new_seed_len, &new_seed_creditable) < 0) { |
| - | bb_perror_msg("can't%s seed", " read new"); |
| - | new_seed_len = SHA256_OUTSIZE; |
| - | memset(new_seed, 0, SHA256_OUTSIZE); |
| - | program_ret |= 1 << 3; |
| - | } |
| + | new_seed_creditable = read_new_seed(new_seed, new_seed_len); |
| sha256_hash(&hash, &new_seed_len, sizeof(new_seed_len)); | |
| sha256_hash(&hash, new_seed, new_seed_len); | |
| sha256_end(&hash, new_seed + new_seed_len - SHA256_OUTSIZE); | |
| - | printf("Saving %u bits of %screditable seed for next boot\n", (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-"); |
| + | printf("Saving %u bits of %screditable seed for next boot\n", |
| + | (unsigned)new_seed_len * 8, new_seed_creditable ? "" : "non-"); |
| fd = open(NON_CREDITABLE_SEED_NAME, O_WRONLY | O_CREAT | O_TRUNC, 0400); | |
| if (fd < 0 || full_write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) { | |
| bb_perror_msg("can't%s seed", " write"); | |