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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include "sd-id128.h"
#include "alloc-util.h"
#include "fd-util.h"
#include "io-util.h"
#include "log.h"
#include "mkdir.h"
#include "string-util.h"
#include "util.h"
#define POOL_SIZE_MIN 512
#define POOL_SIZE_MAX (10*1024*1024)
int main(int argc, char *argv[]) {
_cleanup_close_ int seed_fd = -1, random_fd = -1;
bool read_seed_file, write_seed_file;
_cleanup_free_ void* buf = NULL;
size_t buf_size = 0;
struct stat st;
ssize_t k;
FILE *f;
int r;
if (argc != 2) {
log_error("This program requires one argument.");
return EXIT_FAILURE;
}
log_set_target(LOG_TARGET_AUTO);
log_parse_environment();
log_open();
umask(0022);
/* Read pool size, if possible */
f = fopen("/proc/sys/kernel/random/poolsize", "re");
if (f) {
if (fscanf(f, "%zu", &buf_size) > 0)
/* poolsize is in bits on 2.6, but we want bytes */
buf_size /= 8;
fclose(f);
}
if (buf_size < POOL_SIZE_MIN)
buf_size = POOL_SIZE_MIN;
r = mkdir_parents_label(RANDOM_SEED, 0755);
if (r < 0) {
log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
goto finish;
}
/* When we load the seed we read it and write it to the device and then immediately update the saved seed with
* new data, to make sure the next boot gets seeded differently. */
if (streq(argv[1], "load")) {
int open_rw_error;
seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
open_rw_error = -errno;
if (seed_fd < 0) {
write_seed_file = false;
seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (seed_fd < 0) {
bool missing = errno == ENOENT;
log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m");
r = log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
errno, "Failed to open " RANDOM_SEED " for reading: %m");
if (missing)
r = 0;
goto finish;
}
} else
write_seed_file = true;
random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
if (random_fd < 0) {
write_seed_file = false;
random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
if (random_fd < 0) {
r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
goto finish;
}
}
read_seed_file = true;
} else if (streq(argv[1], "save")) {
random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (random_fd < 0) {
r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
goto finish;
}
seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
if (seed_fd < 0) {
r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
goto finish;
}
read_seed_file = false;
write_seed_file = true;
} else {
log_error("Unknown verb '%s'.", argv[1]);
r = -EINVAL;
goto finish;
}
if (fstat(seed_fd, &st) < 0) {
r = log_error_errno(errno, "Failed to stat() seed file " RANDOM_SEED ": %m");
goto finish;
}
/* If the seed file is larger than what we expect, then honour the existing size and save/restore as much as it says */
if ((uint64_t) st.st_size > buf_size)
buf_size = MIN(st.st_size, POOL_SIZE_MAX);
buf = malloc(buf_size);
if (!buf) {
r = log_oom();
goto finish;
}
if (read_seed_file) {
sd_id128_t mid;
int z;
k = loop_read(seed_fd, buf, buf_size, false);
if (k < 0)
r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
else if (k == 0) {
r = 0;
log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
} else {
(void) lseek(seed_fd, 0, SEEK_SET);
r = loop_write(random_fd, buf, (size_t) k, false);
if (r < 0)
log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
}
/* Let's also write the machine ID into the random seed. Why? As an extra protection against "golden
* images" that are put together sloppily, i.e. images which are duplicated on multiple systems but
* where the random seed file is not properly reset. Frequently the machine ID is properly reset on
* those systems however (simply because it's easier to notice, if it isn't due to address clashes and
* so on, while random seed equivalence is generally not noticed easily), hence let's simply write the
* machined ID into the random pool too. */
z = sd_id128_get_machine(&mid);
if (z < 0)
log_debug_errno(z, "Failed to get machine ID, ignoring: %m");
else {
z = loop_write(random_fd, &mid, sizeof(mid), false);
if (z < 0)
log_debug_errno(z, "Failed to write machine ID to /dev/urandom, ignoring: %m");
}
}
if (write_seed_file) {
/* This is just a safety measure. Given that we are root and
* most likely created the file ourselves the mode and owner
* should be correct anyway. */
(void) fchmod(seed_fd, 0600);
(void) fchown(seed_fd, 0, 0);
k = loop_read(random_fd, buf, buf_size, false);
if (k < 0) {
r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
goto finish;
}
if (k == 0) {
log_error("Got EOF while reading from /dev/urandom.");
r = -EIO;
goto finish;
}
r = loop_write(seed_fd, buf, (size_t) k, false);
if (r < 0)
log_error_errno(r, "Failed to write new random seed file: %m");
}
finish:
return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}
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