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seedrng: hoist bb_strtoul out of min/max

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- Hoist bb_strtoul out of min/max to prevent quadruple evaluation.
- Don't use separate variables for boottime/realtime.
- Make use of ENABLE_FEATURE_CLEAN_UP where appropriate.
- Order hash initialization after lock taking per Bernhard's taste.
- Add comment description of theory of operation.

function                                             old     new   delta
seed_from_file_if_exists                             533     456     -77
seedrng_main                                        1218    1086    -132
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-209)           Total: -209 bytes
   text	   data	    bss	    dec	    hex	filename
 976445	   4227	   1848	 982520	  efdf8	busybox_old
 976236	   4227	   1848	 982311	  efd27	busybox_unstripped

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
This commit is contained in:
Jason A. Donenfeld 2022-04-20 15:27:29 +02:00 committed by Bernhard Reutner-Fischer
parent 4538578996
commit 31ec481baf
1 changed files with 32 additions and 14 deletions
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46
util-linux/seedrng.c
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@ -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, &timestamp);
sha256_hash(&hash, &timestamp, sizeof(timestamp));
clock_gettime(CLOCK_BOOTTIME, &timestamp);
sha256_hash(&hash, &timestamp, 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;
}