/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include #if USE_SYS_RANDOM_H # include #endif #include #include #include #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 "sync-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(); 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."); 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);