[Buildroot] [PATCH] package/urandom-scripts: actually credit seed files via seedrng
Arnout Vandecappelle
arnout at mind.be
Sun Mar 27 19:36:41 UTC 2022
On 27/03/2022 20:01, James Hilliard wrote:
> On Sat, Mar 26, 2022 at 11:48 PM Jason A. Donenfeld <Jason at zx2c4.com> wrote:
>>
>> 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 buildroot
>> and tweaked as needed: <https://git.zx2c4.com/seedrng/about/>.
>>
>> This commit imports it into buildroot and wires up the init scripts to
>> call it. This also is a significant improvement over the current init
>> script, which doesn't credit entropy and whose hashing in shell scripts
>> is sort of fragile.
>>
>> As seedrng.c is a short tiny C program, we include this here in the
>> package, like a few other packages do. Later we'll investigate adding
>> this to busybox, but for now, this is a good start and a positive step
>> in the right direction.
>>
>> Signed-off-by: Jason A. Donenfeld <Jason at zx2c4.com>
[snip]
>> +#ifndef GRND_INSECURE
>> +#define GRND_INSECURE 0x0004 /* Apparently some headers don't ship with this yet. */
>> +#endif
>> +
>> +#ifndef LOCALSTATEDIR
>> +#define LOCALSTATEDIR "/var/lib"
>> +#endif
>> +#ifndef RUNSTATEDIR
>> +#define RUNSTATEDIR "/var/run"
>> +#endif
>
> Might be a good idea to have runtime env overrides for these to allow easier
> path customization by only having to override the init script in a
> rootfs overlay:
> https://buildroot.org/downloads/manual/manual.html#rootfs-custom
>
> Maybe something similar to the SEEDRNG_SKIP_CREDIT env override would
> make sense for these paths.
I don't know if that makes sense. Dozens of buildroot packages hardocde these
paths already.
Regards,
Arnout
>
>> +
>> +#define SEED_DIR LOCALSTATEDIR "/seedrng"
>> +#define CREDITABLE_SEED SEED_DIR "/seed.credit"
>> +#define NON_CREDITABLE_SEED SEED_DIR "/seed.no-credit"
>> +#define LOCK_FILE RUNSTATEDIR "/seedrng.lock"
>> +
>> +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) {
>> + fprintf(stderr, "WARNING: Unable to determine pool size, falling back to %u bits: %s\n", 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;
>> + } else if (ret < 0 && 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;
>> + fprintf(stderr, "ERROR: Unable to open seed file: %s\n", strerror(errno));
>> + return ret;
>> + }
>> + dfd = open(SEED_DIR, O_DIRECTORY | O_RDONLY);
>> + if (dfd < 0) {
>> + ret = -errno;
>> + close(fd);
>> + fprintf(stderr, "ERROR: Unable to open seed directory: %s\n", strerror(errno));
>> + return ret;
>> + }
>> + seed_len = read(fd, seed, sizeof(seed));
>> + if (seed_len < 0) {
>> + ret = -errno;
>> + fprintf(stderr, "ERROR: Unable to read seed file: %s\n", strerror(errno));
>> + }
>> + close(fd);
>> + if (ret) {
>> + close(dfd);
>> + return ret;
>> + }
>> + if ((unlink(filename) < 0 || fsync(dfd) < 0) && seed_len) {
>> + ret = -errno;
>> + fprintf(stderr, "ERROR: Unable to remove seed after reading, so not seeding: %s\n", 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);
>> +
>> + fprintf(stdout, "Seeding %zd bits %s crediting\n", seed_len * 8, credit ? "and" : "without");
>> + ret = seed_rng(seed, seed_len, credit);
>> + if (ret < 0)
>> + fprintf(stderr, "ERROR: Unable to seed: %s\n", strerror(-ret));
>> + return ret;
>> +}
>> +
>> +static bool skip_credit(void)
>> +{
>> + const char *skip = getenv("SEEDRNG_SKIP_CREDIT");
>> + return skip && (!strcmp(skip, "1") || !strcasecmp(skip, "true") ||
>> + !strcasecmp(skip, "yes") || !strcasecmp(skip, "y"));
>> +}
>> +
>> +int main(int argc __attribute__((unused)), char *argv[] __attribute__((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()) {
>> + fprintf(stderr, "ERROR: This program requires root\n");
>> + return 1;
>> + }
>> +
>> + 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) {
>> + fprintf(stderr, "ERROR: Unable to create \"%s\" directory: %s\n", SEED_DIR, strerror(errno));
>> + return 1;
>> + }
>> +
>> + lock = open(LOCK_FILE, O_WRONLY | O_CREAT, 0000);
>> + if (lock < 0 || flock(lock, LOCK_EX) < 0) {
>> + fprintf(stderr, "ERROR: Unable to open lock file: %s\n", strerror(errno));
>> + return 1;
>> + }
>> +
>> + 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, !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) {
>> + fprintf(stderr, "ERROR: Unable to read new seed: %s\n", 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);
>> +
>> + fprintf(stdout, "Saving %zu bits of %s seed for next boot\n", 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) {
>> + fprintf(stderr, "ERROR: Unable to open seed file for writing: %s\n", strerror(errno));
>> + program_ret |= 1 << 4;
>> + goto out;
>> + }
>> + if (write(fd, new_seed, new_seed_len) != (ssize_t)new_seed_len || fsync(fd) < 0) {
>> + fprintf(stderr, "ERROR: Unable to write seed file: %s\n", strerror(errno));
>> + program_ret |= 1 << 5;
>> + goto out;
>> + }
>> + if (new_seed_creditable && rename(NON_CREDITABLE_SEED, CREDITABLE_SEED) < 0) {
>> + fprintf(stderr, "WARNING: Unable to make new seed creditable: %s\n", strerror(errno));
>> + program_ret |= 1 << 6;
>> + }
>> +out:
>> + close(fd);
>> + close(lock);
>> + return program_ret;
>> +}
>> diff --git a/package/urandom-scripts/urandom-scripts.mk b/package/urandom-scripts/urandom-scripts.mk
>> index 2c09728c46..a5cbb95feb 100644
>> --- a/package/urandom-scripts/urandom-scripts.mk
>> +++ b/package/urandom-scripts/urandom-scripts.mk
>> @@ -4,7 +4,17 @@
>> #
>> ################################################################################
>>
>> +define URANDOM_SCRIPTS_EXTRACT_CMDS
>> + cp $(URANDOM_SCRIPTS_PKGDIR)/seedrng.c $(@D)
>> +endef
>> +
>> +define URANDOM_SCRIPTS_BUILD_CMDS
>> + $(TARGET_CC) $(TARGET_CFLAGS) -std=gnu99 $(TARGET_LDFLAGS) \
>> + $(@D)/seedrng.c -o $(@D)/seedrng
>> +endef
>> +
>> define URANDOM_SCRIPTS_INSTALL_INIT_SYSV
>> + $(INSTALL) -D -m 0755 $(@D)/seedrng $(TARGET_DIR)/sbin/seedrng
>> $(INSTALL) -D -m 0755 $(URANDOM_SCRIPTS_PKGDIR)/S20urandom \
>> $(TARGET_DIR)/etc/init.d/S20urandom
>> endef
>> --
>> 2.35.1
>>
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