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Use seedrng for seeding the random number generator

Browse Source 
The RNG can't actually be seeded from a shell script, due to the
reliance on ioctls. For this reason, the seedrng project provides a
basic script meant to be copy and pasted into projects like OpenRC and
tweaked as needed: https://git.zx2c4.com/seedrng/about/

This commit imports it into OpenRC and wires up /etc/init.d/urandom to
call it. It shouldn't be called by other things on the system, so it
lives in rc_sbindir.

Closes #506.
Closes #507.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-03-24 22:07:16 -06:00 committed by William Hubbs
parent 270e5c6828
commit 076c2552ae
6 changed files with 499 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
AUTHORS
View File

@ -43,6 +43,7 @@ Ian Stakenvicius <axs@gentoo.org>
Jakob Drexel <jake42@rommel.stw.uni-erlangen.de>
James Le Cuirot <chewi@aura-online.co.uk>
Jan Psota <jasiu@belsznica.pl>
Jason A. Donenfeld <Jason@zx2c4.com>
Jason Zaman <jason@perfinion.com>
Joe Harvell <jharvell@dogpad.net>
Joe M <joe9mail@gmail.com>

9
conf.d/urandom
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@ -2,4 +2,11 @@
# (say for crypt swap), so you will need to customize this
# behavior. If you have /var on a separate partition, then
# make sure this path lives on your root device somewhere.
urandom_seed="/var/lib/misc/random-seed"
seed_dir="/var/lib/seedrng"
lock_file="/var/run/seedrng.lock"
# Set this to true if you do not want seed files to actually
# credit the RNG. Set this if you plan to replicate this
# file system image and do not have the wherewithal to first
# delete the contents of /var/lib/seedrng.
skip_credit="false"

41
init.d/urandom.in
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@ -1,5 +1,5 @@
#!@SBINDIR@/openrc-run
# Copyright (c) 2007-2015 The OpenRC Authors.
# Copyright (c) 2007-2022 The OpenRC Authors.
# See the Authors file at the top-level directory of this distribution and
# https://github.com/OpenRC/openrc/blob/HEAD/AUTHORS
#
@ -9,7 +9,10 @@
# This file may not be copied, modified, propagated, or distributed
# except according to the terms contained in the LICENSE file.
: ${urandom_seed:=${URANDOM_SEED:-/var/lib/misc/random-seed}}
export SEEDRNG_SEED_DIR="${seed_dir:-/var/lib/seedrng}"
export SEEDRNG_LOCK_FILE="${lock_file:-/var/run/seedrng.lock}"
export SEEDRNG_SKIP_CREDIT="${skip_credit:-false}"
: ${urandom_seed:=${SEEDRNG_SEED_DIR}/../misc/random-seed}
description="Initializes the random number generator."
depend()
@ -21,33 +24,35 @@ depend()
save_seed()
{
local psz=1
if [ -e /proc/sys/kernel/random/poolsize ]; then
: $(( psz = $(cat /proc/sys/kernel/random/poolsize) / 4096 ))
fi
( # sub shell to prevent umask pollution
umask 077
dd if=/dev/urandom of="$urandom_seed" count=${psz} 2>/dev/null
dd if=/dev/urandom of="$urandom_seed" count=1 2>/dev/null
)
}
start()
{
[ -c /dev/urandom ] || return
if [ -f "$urandom_seed" ]; then
ebegin "Initializing random number generator"
cat "$urandom_seed" > /dev/urandom
eend $? "Error initializing random number generator"
if [ "$RC_UNAME" = Linux ]; then
seedrng
else
[ -c /dev/urandom ] || return
if [ -f "$urandom_seed" ]; then
ebegin "Initializing random number generator"
cat "$urandom_seed" > /dev/urandom
eend $? "Error initializing random number generator"
fi
rm -f "$urandom_seed" && save_seed
fi
rm -f "$urandom_seed" && save_seed
return 0
}
stop()
{
ebegin "Saving random seed"
save_seed
eend $? "Failed to save random seed"
if [ "$RC_UNAME" = Linux ]; then
seedrng
else
ebegin "Saving random seed"
save_seed
eend $? "Failed to save random seed"
fi
}

6
src/rc/Makefile
View File

@ -15,7 +15,7 @@ endif
ifeq (${OS},Linux)
SRCS+= kill_all.c openrc-init.c openrc-shutdown.c rc-sysvinit.c broadcast.c \
rc-wtmp.c
rc-wtmp.c seedrng.c
endif
CLEANFILES= version.h rc-selinux.o
@ -47,6 +47,7 @@ RC_SBINPROGS= mark_service_starting mark_service_started \
ifeq (${OS},Linux)
RC_BINPROGS+= kill_all
RC_SBINPROGS+= seedrng
SBINPROGS+= openrc-init openrc-shutdown
endif
@ -180,3 +181,6 @@ shell_var: shell_var.o
swclock: swclock.o _usage.o rc-misc.o
${CC} ${LOCAL_CFLAGS} ${LOCAL_LDFLAGS} ${CFLAGS} ${LDFLAGS} -o $@ $^ ${LDADD}
seedrng: seedrng.o
${CC} ${LOCAL_CFLAGS} ${LOCAL_LDFLAGS} ${CFLAGS} ${LDFLAGS} -o $@ $^ ${LDADD}

10
src/rc/meson.build
View File

@ -268,7 +268,15 @@ if os == 'Linux'
link_with: [libeinfo,librc],
install: true,
install_dir: rc_bindir)
endif
executable('seedrng',
['seedrng.c'],
c_args : cc_branding_flags,
include_directories: [incdir, einfo_incdir, rc_incdir],
link_with: [libeinfo, librc],
install: true,
install_dir: rc_sbindir)
endif
executable('shell_var',
['shell_var.c'],

453
src/rc/seedrng.c Normal file
View File

@ -0,0 +1,453 @@
/*
* seedrng.c
* Seed kernel RNG from seed file, based on code from:
* https://git.zx2c4.com/seedrng/about/
*/
/*
* Copyright (c) 2022 The OpenRC Authors.
* See the Authors file at the top-level directory of this distribution and
* https://github.com/OpenRC/openrc/blob/HEAD/AUTHORS
*
* This file is part of OpenRC. It is subject to the license terms in
* the LICENSE file found in the top-level directory of this
* distribution and at https://github.com/OpenRC/openrc/blob/HEAD/LICENSE
* This file may not be copied, modified, propagated, or distributed
* except according to the terms contained in the LICENSE file.
*/
#include <linux/random.h>
#include <sys/random.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <poll.h>
#include <unistd.h>
#include <time.h>
#include <errno.h>
#include <endian.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include "rc.h"
#include "einfo.h"
#include "helpers.h"
#ifndef GRND_INSECURE
#define GRND_INSECURE 0x0004 /* Apparently some headers don't ship with this yet. */
#endif
static const char *SEED_DIR;
static const char *LOCK_FILE;
static char *CREDITABLE_SEED;
static char *NON_CREDITABLE_SEED;
enum blake2s_lengths {
BLAKE2S_BLOCK_LEN = 64,
BLAKE2S_HASH_LEN = 32,
BLAKE2S_KEY_LEN = 32
};
enum seedrng_lengths {
MAX_SEED_LEN = 512,
MIN_SEED_LEN = BLAKE2S_HASH_LEN
};
struct blake2s_state {
uint32_t h[8];
uint32_t t[2];
uint32_t f[2];
uint8_t buf[BLAKE2S_BLOCK_LEN];
unsigned int buflen;
unsigned int outlen;
};
#define le32_to_cpup(a) le32toh(*(a))
#define cpu_to_le32(a) htole32(a)
#ifndef ARRAY_SIZE
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#endif
#ifndef DIV_ROUND_UP
#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
#endif
static inline void cpu_to_le32_array(uint32_t *buf, unsigned int words)
{
while (words--) {
*buf = cpu_to_le32(*buf);
++buf;
}
}
static inline void le32_to_cpu_array(uint32_t *buf, unsigned int words)
{
while (words--) {
*buf = le32_to_cpup(buf);
++buf;
}
}
static inline uint32_t ror32(uint32_t word, unsigned int shift)
{
return (word >> (shift & 31)) | (word << ((-shift) & 31));
}
static const uint32_t blake2s_iv[8] = {
0x6A09E667UL, 0xBB67AE85UL, 0x3C6EF372UL, 0xA54FF53AUL,
0x510E527FUL, 0x9B05688CUL, 0x1F83D9ABUL, 0x5BE0CD19UL
};
static const uint8_t blake2s_sigma[10][16] = {
{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },
{ 14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3 },
{ 11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4 },
{ 7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8 },
{ 9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13 },
{ 2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9 },
{ 12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11 },
{ 13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10 },
{ 6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5 },
{ 10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0 },
};
static void blake2s_set_lastblock(struct blake2s_state *state)
{
state->f[0] = -1;
}
static void blake2s_increment_counter(struct blake2s_state *state, const uint32_t inc)
{
state->t[0] += inc;
state->t[1] += (state->t[0] < inc);
}
static void blake2s_init_param(struct blake2s_state *state, const uint32_t param)
{
int i;
memset(state, 0, sizeof(*state));
for (i = 0; i < 8; ++i)
state->h[i] = blake2s_iv[i];
state->h[0] ^= param;
}
static void blake2s_init(struct blake2s_state *state, const size_t outlen)
{
blake2s_init_param(state, 0x01010000 | outlen);
state->outlen = outlen;
}
static void blake2s_compress(struct blake2s_state *state, const uint8_t *block, size_t nblocks, const uint32_t inc)
{
uint32_t m[16];
uint32_t v[16];
int i;
while (nblocks > 0) {
blake2s_increment_counter(state, inc);
memcpy(m, block, BLAKE2S_BLOCK_LEN);
le32_to_cpu_array(m, ARRAY_SIZE(m));
memcpy(v, state->h, 32);
v[ 8] = blake2s_iv[0];
v[ 9] = blake2s_iv[1];
v[10] = blake2s_iv[2];
v[11] = blake2s_iv[3];
v[12] = blake2s_iv[4] ^ state->t[0];
v[13] = blake2s_iv[5] ^ state->t[1];
v[14] = blake2s_iv[6] ^ state->f[0];
v[15] = blake2s_iv[7] ^ state->f[1];
#define G(r, i, a, b, c, d) do { \
a += b + m[blake2s_sigma[r][2 * i + 0]]; \
d = ror32(d ^ a, 16); \
c += d; \
b = ror32(b ^ c, 12); \
a += b + m[blake2s_sigma[r][2 * i + 1]]; \
d = ror32(d ^ a, 8); \
c += d; \
b = ror32(b ^ c, 7); \
} while (0)
#define ROUND(r) do { \
G(r, 0, v[0], v[ 4], v[ 8], v[12]); \
G(r, 1, v[1], v[ 5], v[ 9], v[13]); \
G(r, 2, v[2], v[ 6], v[10], v[14]); \
G(r, 3, v[3], v[ 7], v[11], v[15]); \
G(r, 4, v[0], v[ 5], v[10], v[15]); \
G(r, 5, v[1], v[ 6], v[11], v[12]); \
G(r, 6, v[2], v[ 7], v[ 8], v[13]); \
G(r, 7, v[3], v[ 4], v[ 9], v[14]); \
} while (0)
ROUND(0);
ROUND(1);
ROUND(2);
ROUND(3);
ROUND(4);
ROUND(5);
ROUND(6);
ROUND(7);
ROUND(8);
ROUND(9);
#undef G
#undef ROUND
for (i = 0; i < 8; ++i)
state->h[i] ^= v[i] ^ v[i + 8];
block += BLAKE2S_BLOCK_LEN;
--nblocks;
}
}
static void blake2s_update(struct blake2s_state *state, const void *inp, size_t inlen)
{
const size_t fill = BLAKE2S_BLOCK_LEN - state->buflen;
const uint8_t *in = inp;
if (!inlen)
return;
if (inlen > fill) {
memcpy(state->buf + state->buflen, in, fill);
blake2s_compress(state, state->buf, 1, BLAKE2S_BLOCK_LEN);
state->buflen = 0;
in += fill;
inlen -= fill;
}
if (inlen > BLAKE2S_BLOCK_LEN) {
const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_LEN);
blake2s_compress(state, in, nblocks - 1, BLAKE2S_BLOCK_LEN);
in += BLAKE2S_BLOCK_LEN * (nblocks - 1);
inlen -= BLAKE2S_BLOCK_LEN * (nblocks - 1);
}
memcpy(state->buf + state->buflen, in, inlen);
state->buflen += inlen;
}
static void blake2s_final(struct blake2s_state *state, uint8_t *out)
{
blake2s_set_lastblock(state);
memset(state->buf + state->buflen, 0, BLAKE2S_BLOCK_LEN - state->buflen);
blake2s_compress(state, state->buf, 1, state->buflen);
cpu_to_le32_array(state->h, ARRAY_SIZE(state->h));
memcpy(out, state->h, state->outlen);
}
static size_t determine_optimal_seed_len(void)
{
size_t ret = 0;
char poolsize_str[11] = { 0 };
int fd = open("/proc/sys/kernel/random/poolsize", O_RDONLY);
if (fd < 0 || read(fd, poolsize_str, sizeof(poolsize_str) - 1) < 0) {
ewarn("Unable to determine pool size, falling back to %u bits: %s", MIN_SEED_LEN * 8, strerror(errno));
ret = MIN_SEED_LEN;
} else
ret = DIV_ROUND_UP(strtoul(poolsize_str, NULL, 10), 8);
if (fd >= 0)
close(fd);
if (ret < MIN_SEED_LEN)
ret = MIN_SEED_LEN;
else if (ret > MAX_SEED_LEN)
ret = MAX_SEED_LEN;
return ret;
}
static int read_new_seed(uint8_t *seed, size_t len, bool *is_creditable)
{
ssize_t ret;
int urandom_fd;
*is_creditable = false;
ret = getrandom(seed, len, GRND_NONBLOCK);
if (ret == (ssize_t)len) {
*is_creditable = true;
return 0;
}
if (ret == -1 && errno == ENOSYS) {
struct pollfd random_fd = {
.fd = open("/dev/random", O_RDONLY),
.events = POLLIN
};
if (random_fd.fd < 0)
return -errno;
*is_creditable = poll(&random_fd, 1, 0) == 1;
close(random_fd.fd);
} else if (getrandom(seed, len, GRND_INSECURE) == (ssize_t)len)
return 0;
urandom_fd = open("/dev/urandom", O_RDONLY);
if (urandom_fd < 0)
return -errno;
ret = read(urandom_fd, seed, len);
if (ret == (ssize_t)len)
ret = 0;
else
ret = -errno ? -errno : -EIO;
close(urandom_fd);
return ret;
}
static int seed_rng(uint8_t *seed, size_t len, bool credit)
{
struct {
int entropy_count;
int buf_size;
uint8_t buffer[MAX_SEED_LEN];
} req = {
.entropy_count = credit ? len * 8 : 0,
.buf_size = len
};
int random_fd, ret;
if (len > sizeof(req.buffer))
return -EFBIG;
memcpy(req.buffer, seed, len);
random_fd = open("/dev/random", O_RDWR);
if (random_fd < 0)
return -errno;
ret = ioctl(random_fd, RNDADDENTROPY, &req);
if (ret)
ret = -errno ? -errno : -EIO;
close(random_fd);
return ret;
}
static int seed_from_file_if_exists(const char *filename, bool credit, struct blake2s_state *hash)
{
uint8_t seed[MAX_SEED_LEN];
ssize_t seed_len;
int fd, dfd, ret = 0;
fd = open(filename, O_RDONLY);
if (fd < 0 && errno == ENOENT)
return 0;
else if (fd < 0) {
ret = -errno;
eerror("Unable to open seed file: %s", strerror(errno));
return ret;
}
dfd = open(SEED_DIR, O_DIRECTORY | O_RDONLY);
if (dfd < 0) {
ret = -errno;
close(fd);
eerror("Unable to open seed directory: %s", strerror(errno));
return ret;
}
seed_len = read(fd, seed, sizeof(seed));
if (seed_len < 0) {
ret = -errno;
eerror("Unable to read seed file: %s", strerror(errno));
}
close(fd);
if (ret) {
close(dfd);
return ret;
}
if ((unlink(filename) < 0 || fsync(dfd) < 0) && seed_len) {
ret = -errno;
eerror("Unable to remove seed after reading, so not seeding: %s", strerror(errno));
}
close(dfd);
if (ret)
return ret;
if (!seed_len)
return 0;
blake2s_update(hash, &seed_len, sizeof(seed_len));
blake2s_update(hash, seed, seed_len);
einfo("Seeding %zd bits %s crediting", seed_len * 8, credit ? "and" : "without");
ret = seed_rng(seed, seed_len, credit);
if (ret < 0)
eerror("Unable to seed: %s", strerror(-ret));
return ret;
}
static void populate_global_paths(void)
{
SEED_DIR = getenv("SEEDRNG_SEED_DIR");
if (!SEED_DIR || !*SEED_DIR)
SEED_DIR = "/var/lib/seedrng";
LOCK_FILE = getenv("SEEDRNG_LOCK_FILE");
if (!LOCK_FILE || !*LOCK_FILE)
LOCK_FILE = "/var/run/seedrng.lock";
xasprintf(&CREDITABLE_SEED, "%s/seed.credit", SEED_DIR);
xasprintf(&NON_CREDITABLE_SEED, "%s/seed.no-credit", SEED_DIR);
}
int main(int argc _unused, char *argv[] _unused)
{
static const char seedrng_prefix[] = "SeedRNG v1 Old+New Prefix";
static const char seedrng_failure[] = "SeedRNG v1 No New Seed Failure";
int ret, fd, lock, program_ret = 0;
uint8_t new_seed[MAX_SEED_LEN];
size_t new_seed_len;
bool new_seed_creditable;
struct timespec realtime = { 0 }, boottime = { 0 };
struct blake2s_state hash;
umask(0077);
if (getuid())
eerrorx("This rc helper program requires root");
populate_global_paths();
blake2s_init(&hash, BLAKE2S_HASH_LEN);
blake2s_update(&hash, seedrng_prefix, strlen(seedrng_prefix));
clock_gettime(CLOCK_REALTIME, &realtime);
clock_gettime(CLOCK_BOOTTIME, &boottime);
blake2s_update(&hash, &realtime, sizeof(realtime));
blake2s_update(&hash, &boottime, sizeof(boottime));
if (mkdir(SEED_DIR, 0700) < 0 && errno != EEXIST)
eerrorx("Unable to create \"%s\" directory: %s", SEED_DIR, strerror(errno));
lock = open(LOCK_FILE, O_WRONLY | O_CREAT, 0000);
if (lock < 0 || flock(lock, LOCK_EX) < 0)
eerrorx("Unable to open lock file: %s", strerror(errno));
ret = seed_from_file_if_exists(NON_CREDITABLE_SEED, false, &hash);
if (ret < 0)
program_ret |= 1 << 1;
ret = seed_from_file_if_exists(CREDITABLE_SEED, !rc_yesno(getenv("SEEDRNG_SKIP_CREDIT")), &hash);
if (ret < 0)
program_ret |= 1 << 2;
new_seed_len = determine_optimal_seed_len();
ret = read_new_seed(new_seed, new_seed_len, &new_seed_creditable);
if (ret < 0) {
eerror("Unable to read new seed: %s", strerror(-ret));
new_seed_len = BLAKE2S_HASH_LEN;
strncpy((char *)new_seed, seedrng_failure, new_seed_len);
program_ret |= 1 << 3;
}
blake2s_update(&hash, &new_seed_len, sizeof(new_seed_len));
blake2s_update(&hash, new_seed, new_seed_len);
blake2s_final(&hash, new_seed + new_seed_len - BLAKE2S_HASH_LEN);
einfo("Saving %zu bits of %s seed for next boot", new_seed_len * 8, new_seed_creditable ? "creditable" : "non-creditable");
fd = open(NON_CREDITABLE_SEED, O_WRONLY | O_CREAT | O_TRUNC, 0400);
if (fd < 0) {
eerror("Unable to open seed file for writing: %s", strerror(errno));
program_ret |= 1 << 4;
goto out;
}
if (write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
eerror("Unable to write seed file: %s", strerror(errno));
program_ret |= 1 << 5;
goto out;
}
if (new_seed_creditable && rename(NON_CREDITABLE_SEED, CREDITABLE_SEED) < 0) {
ewarn("Unable to make new seed creditable: %s", strerror(errno));
program_ret |= 1 << 6;
}
out:
close(fd);
close(lock);
return program_ret;
}