diff options
| -rw-r--r-- | util-linux/seedrng.c | 46 |
1 files changed, 32 insertions, 14 deletions
diff --git a/util-linux/seedrng.c b/util-linux/seedrng.c index d82a942..1bceae4 100644 --- a/util-linux/seedrng.c +++ b/util-linux/seedrng.c @@ -2,11 +2,26 @@ /* * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. * + * SeedRNG is a simple program made for seeding the Linux kernel random number + * generator from seed files. It is is useful in light of the fact that the + * Linux kernel RNG cannot be initialized from shell scripts, and new seeds + * cannot be safely generated from boot time shell scripts either. It should + * be run once at init time and once at shutdown time. It can be run at other + * times on a timer as well. Whenever it is run, it writes existing seed files + * into the RNG pool, and then creates a new seed file. If the RNG is + * initialized at the time of creating a new seed file, then that new seed file + * is marked as "creditable", which means it can be used to initialize the RNG. + * Otherwise, it is marked as "non-creditable", in which case it is still used + * to seed the RNG's pool, but will not initialize the RNG. In order to ensure + * that entropy only ever stays the same or increases from one seed file to the + * next, old seed values are hashed together with new seed values when writing + * new seed files. + * * This is based on code from <https://git.zx2c4.com/seedrng/about/>. */ //config:config SEEDRNG -//config: bool "seedrng (2.6 kb)" +//config: bool "seedrng (2.5 kb)" //config: default y //config: help //config: Seed the kernel RNG from seed files, meant to be called @@ -71,12 +86,14 @@ enum seedrng_lengths { static size_t determine_optimal_seed_len(void) { char poolsize_str[11] = { 0 }; + unsigned long poolsize; if (open_read_close("/proc/sys/kernel/random/poolsize", poolsize_str, sizeof(poolsize_str) - 1) < 0) { bb_perror_msg("unable to determine pool size, falling back to %u bits", MIN_SEED_LEN * 8); return MIN_SEED_LEN; } - return MAX(MIN((bb_strtoul(poolsize_str, NULL, 10) + 7) / 8, MAX_SEED_LEN), MIN_SEED_LEN); + poolsize = (bb_strtoul(poolsize_str, NULL, 10) + 7) / 8; + return MAX(MIN(poolsize, MAX_SEED_LEN), MIN_SEED_LEN); } static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable) @@ -130,7 +147,8 @@ static int seed_rng(uint8_t *seed, size_t len, bool credit) ret = ioctl(random_fd, RNDADDENTROPY, &req); if (ret) ret = -errno ? -errno : -EIO; - close(random_fd); + if (ENABLE_FEATURE_CLEAN_UP) + close(random_fd); errno = -ret; return ret ? -1 : 0; } @@ -171,7 +189,7 @@ static int seed_from_file_if_exists(const char *filename, bool credit, sha256_ct if (ret < 0) bb_simple_perror_msg("unable to seed"); out: - if (dfd >= 0) + if (ENABLE_FEATURE_CLEAN_UP && dfd >= 0) close(dfd); errno = -ret; return ret ? -1 : 0; @@ -187,7 +205,7 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) size_t new_seed_len; bool new_seed_creditable; bool skip_credit = false; - struct timespec realtime = { 0 }, boottime = { 0 }; + struct timespec timestamp = { 0 }; sha256_ctx_t hash; int opt; @@ -217,13 +235,6 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) if (getuid()) bb_simple_error_msg_and_die("this program requires root"); - sha256_begin(&hash); - sha256_hash(&hash, seedrng_prefix, strlen(seedrng_prefix)); - clock_gettime(CLOCK_REALTIME, &realtime); - clock_gettime(CLOCK_BOOTTIME, &boottime); - sha256_hash(&hash, &realtime, sizeof(realtime)); - sha256_hash(&hash, &boottime, sizeof(boottime)); - if (mkdir(seed_dir, 0700) < 0 && errno != EEXIST) bb_simple_perror_msg_and_die("unable to create seed directory"); @@ -234,6 +245,13 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) goto out; } + sha256_begin(&hash); + sha256_hash(&hash, seedrng_prefix, strlen(seedrng_prefix)); + clock_gettime(CLOCK_REALTIME, ×tamp); + sha256_hash(&hash, ×tamp, sizeof(timestamp)); + clock_gettime(CLOCK_BOOTTIME, ×tamp); + sha256_hash(&hash, ×tamp, sizeof(timestamp)); + ret = seed_from_file_if_exists(non_creditable_seed, false, &hash); if (ret < 0) program_ret |= 1 << 1; @@ -270,9 +288,9 @@ int seedrng_main(int argc UNUSED_PARAM, char *argv[]) program_ret |= 1 << 6; } out: - if (fd >= 0) + if (ENABLE_FEATURE_CLEAN_UP && fd >= 0) close(fd); - if (lock >= 0) + if (ENABLE_FEATURE_CLEAN_UP && lock >= 0) close(lock); return program_ret; } |