31ec481ba
Jason A. Donenfeld
2022-04-20
Subject
seedrng: hoist bb_strtoul out of min/max
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util-linux/seedrng.c+32 -14
| @@ -2,11 +2,26 @@ | |
| /* | |
| * Copyright (C) 2022 Jason A. Donenfeld <[email protected]>. 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; | |
| } | |