| /* SPDX-License-Identifier: LGPL-2.1+ */ |
| |
| #include <errno.h> |
| #include <fcntl.h> |
| #include <linux/random.h> |
| #include <sys/ioctl.h> |
| #if USE_SYS_RANDOM_H |
| # include <sys/random.h> |
| #endif |
| #include <sys/stat.h> |
| #include <sys/xattr.h> |
| #include <unistd.h> |
| |
| #include "sd-id128.h" |
| |
| #include "alloc-util.h" |
| #include "fd-util.h" |
| #include "fs-util.h" |
| #include "io-util.h" |
| #include "log.h" |
| #include "main-func.h" |
| #include "missing_random.h" |
| #include "missing_syscall.h" |
| #include "mkdir.h" |
| #include "parse-util.h" |
| #include "random-util.h" |
| #include "string-util.h" |
| #include "util.h" |
| #include "xattr-util.h" |
| |
| typedef enum CreditEntropy { |
| CREDIT_ENTROPY_NO_WAY, |
| CREDIT_ENTROPY_YES_PLEASE, |
| CREDIT_ENTROPY_YES_FORCED, |
| } CreditEntropy; |
| |
| static CreditEntropy may_credit(int seed_fd) { |
| _cleanup_free_ char *creditable = NULL; |
| const char *e; |
| int r; |
| |
| assert(seed_fd >= 0); |
| |
| e = getenv("SYSTEMD_RANDOM_SEED_CREDIT"); |
| if (!e) { |
| log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is not set, not crediting entropy."); |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| if (streq(e, "force")) { |
| log_debug("$SYSTEMD_RANDOM_SEED_CREDIT is set to 'force', crediting entropy."); |
| return CREDIT_ENTROPY_YES_FORCED; |
| } |
| |
| r = parse_boolean(e); |
| if (r <= 0) { |
| if (r < 0) |
| log_warning_errno(r, "Failed to parse $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy: %m"); |
| else |
| log_debug("Crediting entropy is turned off via $SYSTEMD_RANDOM_SEED_CREDIT, not crediting entropy."); |
| |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| |
| /* Determine if the file is marked as creditable */ |
| r = fgetxattr_malloc(seed_fd, "user.random-seed-creditable", &creditable); |
| if (r < 0) { |
| if (IN_SET(r, -ENODATA, -ENOSYS, -EOPNOTSUPP)) |
| log_debug_errno(r, "Seed file is not marked as creditable, not crediting."); |
| else |
| log_warning_errno(r, "Failed to read extended attribute, ignoring: %m"); |
| |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| |
| r = parse_boolean(creditable); |
| if (r <= 0) { |
| if (r < 0) |
| log_warning_errno(r, "Failed to parse user.random-seed-creditable extended attribute, ignoring: %s", creditable); |
| else |
| log_debug("Seed file is marked as not creditable, not crediting."); |
| |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| |
| /* Don't credit the random seed if we are in first-boot mode, because we are supposed to start from |
| * scratch. This is a safety precaution for cases where we people ship "golden" images with empty |
| * /etc but populated /var that contains a random seed. */ |
| if (access("/run/systemd/first-boot", F_OK) < 0) { |
| |
| if (errno != ENOENT) { |
| log_warning_errno(errno, "Failed to check whether we are in first-boot mode, not crediting entropy: %m"); |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| |
| /* If ENOENT all is good, we are not in first-boot mode. */ |
| } else { |
| log_debug("Not crediting entropy, since booted in first-boot mode."); |
| return CREDIT_ENTROPY_NO_WAY; |
| } |
| |
| return CREDIT_ENTROPY_YES_PLEASE; |
| } |
| |
| static int run(int argc, char *argv[]) { |
| _cleanup_close_ int seed_fd = -1, random_fd = -1; |
| bool read_seed_file, write_seed_file, synchronous; |
| _cleanup_free_ void* buf = NULL; |
| size_t buf_size; |
| struct stat st; |
| ssize_t k; |
| int r; |
| |
| log_setup_service(); |
| |
| if (argc != 2) |
| return log_error_errno(SYNTHETIC_ERRNO(EINVAL), |
| "This program requires one argument."); |
| |
| umask(0022); |
| |
| buf_size = random_pool_size(); |
| |
| r = mkdir_parents(RANDOM_SEED, 0755); |
| if (r < 0) |
| return log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m"); |
| |
| /* 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")) { |
| |
| seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
| if (seed_fd < 0) { |
| int open_rw_error = -errno; |
| |
| 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"); |
| return missing ? 0 : r; |
| } |
| } else |
| write_seed_file = true; |
| |
| random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600); |
| if (random_fd < 0) |
| return log_error_errno(errno, "Failed to open /dev/urandom: %m"); |
| |
| read_seed_file = true; |
| synchronous = true; /* make this invocation a synchronous barrier for random pool initialization */ |
| |
| } else if (streq(argv[1], "save")) { |
| |
| random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); |
| if (random_fd < 0) |
| return log_error_errno(errno, "Failed to open /dev/urandom: %m"); |
| |
| seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600); |
| if (seed_fd < 0) |
| return log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m"); |
| |
| read_seed_file = false; |
| write_seed_file = true; |
| synchronous = false; |
| } else |
| return log_error_errno(SYNTHETIC_ERRNO(EINVAL), |
| "Unknown verb '%s'.", argv[1]); |
| |
| if (fstat(seed_fd, &st) < 0) |
| return log_error_errno(errno, "Failed to stat() seed file " RANDOM_SEED ": %m"); |
| |
| /* 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, RANDOM_POOL_SIZE_MAX); |
| |
| buf = malloc(buf_size); |
| if (!buf) |
| return log_oom(); |
| |
| if (read_seed_file) { |
| sd_id128_t mid; |
| |
| /* First, let's write the machine ID into /dev/urandom, not crediting entropy. 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. */ |
| r = sd_id128_get_machine(&mid); |
| if (r < 0) |
| log_debug_errno(r, "Failed to get machine ID, ignoring: %m"); |
| else { |
| r = loop_write(random_fd, &mid, sizeof(mid), false); |
| if (r < 0) |
| log_debug_errno(r, "Failed to write machine ID to /dev/urandom, ignoring: %m"); |
| } |
| |
| k = loop_read(seed_fd, buf, buf_size, false); |
| if (k < 0) |
| log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m"); |
| else if (k == 0) |
| log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding."); |
| else { |
| CreditEntropy lets_credit; |
| |
| (void) lseek(seed_fd, 0, SEEK_SET); |
| |
| lets_credit = may_credit(seed_fd); |
| |
| /* Before we credit or use the entropy, let's make sure to securely drop the |
| * creditable xattr from the file, so that we never credit the same random seed |
| * again. Note that further down we'll write a new seed again, and likely mark it as |
| * credible again, hence this is just paranoia to close the short time window between |
| * the time we upload the random seed into the kernel and download the new one from |
| * it. */ |
| |
| if (fremovexattr(seed_fd, "user.random-seed-creditable") < 0) { |
| if (!IN_SET(errno, ENODATA, ENOSYS, EOPNOTSUPP)) |
| log_warning_errno(errno, "Failed to remove extended attribute, ignoring: %m"); |
| |
| /* Otherwise, there was no creditable flag set, which is OK. */ |
| } else { |
| r = fsync_full(seed_fd); |
| if (r < 0) { |
| log_warning_errno(r, "Failed to synchronize seed to disk, not crediting entropy: %m"); |
| |
| if (lets_credit == CREDIT_ENTROPY_YES_PLEASE) |
| lets_credit = CREDIT_ENTROPY_NO_WAY; |
| } |
| } |
| |
| r = random_write_entropy(random_fd, buf, k, |
| IN_SET(lets_credit, CREDIT_ENTROPY_YES_PLEASE, CREDIT_ENTROPY_YES_FORCED)); |
| if (r < 0) |
| log_error_errno(r, "Failed to write seed to /dev/urandom: %m"); |
| } |
| } |
| |
| if (write_seed_file) { |
| bool getrandom_worked = false; |
| |
| /* 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. */ |
| r = fchmod_and_chown(seed_fd, 0600, 0, 0); |
| if (r < 0) |
| return log_error_errno(r, "Failed to adjust seed file ownership and access mode."); |
| |
| /* Let's make this whole job asynchronous, i.e. let's make ourselves a barrier for |
| * proper initialization of the random pool. */ |
| k = getrandom(buf, buf_size, GRND_NONBLOCK); |
| if (k < 0 && errno == EAGAIN && synchronous) { |
| log_notice("Kernel entropy pool is not initialized yet, waiting until it is."); |
| k = getrandom(buf, buf_size, 0); /* retry synchronously */ |
| } |
| if (k < 0) |
| log_debug_errno(errno, "Failed to read random data with getrandom(), falling back to /dev/urandom: %m"); |
| else if ((size_t) k < buf_size) |
| log_debug("Short read from getrandom(), falling back to /dev/urandom: %m"); |
| else |
| getrandom_worked = true; |
| |
| if (!getrandom_worked) { |
| /* Retry with classic /dev/urandom */ |
| k = loop_read(random_fd, buf, buf_size, false); |
| if (k < 0) |
| return log_error_errno(k, "Failed to read new seed from /dev/urandom: %m"); |
| if (k == 0) |
| return log_error_errno(SYNTHETIC_ERRNO(EIO), |
| "Got EOF while reading from /dev/urandom."); |
| } |
| |
| r = loop_write(seed_fd, buf, (size_t) k, false); |
| if (r < 0) |
| return log_error_errno(r, "Failed to write new random seed file: %m"); |
| |
| if (ftruncate(seed_fd, k) < 0) |
| return log_error_errno(r, "Failed to truncate random seed file: %m"); |
| |
| r = fsync_full(seed_fd); |
| if (r < 0) |
| return log_error_errno(r, "Failed to synchronize seed file: %m"); |
| |
| /* If we got this random seed data from getrandom() the data is suitable for crediting |
| * entropy later on. Let's keep that in mind by setting an extended attribute. on the file */ |
| if (getrandom_worked) |
| if (fsetxattr(seed_fd, "user.random-seed-creditable", "1", 1, 0) < 0) |
| log_full_errno(ERRNO_IS_NOT_SUPPORTED(errno) ? LOG_DEBUG : LOG_WARNING, errno, |
| "Failed to mark seed file as creditable, ignoring: %m"); |
| } |
| |
| return 0; |
| } |
| |
| DEFINE_MAIN_FUNCTION(run); |