diff options
Diffstat (limited to 'src/random-seed')
| -rw-r--r-- | src/random-seed/random-seed.c | 225 |
1 files changed, 191 insertions, 34 deletions
diff --git a/src/random-seed/random-seed.c b/src/random-seed/random-seed.c index dc148ebc86..cbc9745584 100644 --- a/src/random-seed/random-seed.c +++ b/src/random-seed/random-seed.c @@ -2,8 +2,14 @@ #include <errno.h> #include <fcntl.h> +#include <linux/random.h> #include <string.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" @@ -14,14 +20,90 @@ #include "io-util.h" #include "log.h" #include "main-func.h" +#include "missing.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; + bool read_seed_file, write_seed_file, synchronous; _cleanup_free_ void* buf = NULL; size_t buf_size; struct stat st; @@ -71,6 +153,7 @@ static int run(int argc, char *argv[]) { 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")) { @@ -84,7 +167,7 @@ static int run(int argc, char *argv[]) { read_seed_file = false; write_seed_file = true; - + synchronous = false; } else return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Unknown verb '%s'.", argv[1]); @@ -102,57 +185,131 @@ static int run(int argc, char *argv[]) { if (read_seed_file) { sd_id128_t mid; - int z; + + /* 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) - r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m"); - else if (k == 0) { - r = 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 { + else { + CreditEntropy lets_credit; + (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"); - } + lets_credit = may_credit(seed_fd); - /* 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"); + /* 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; + } + } + + if (IN_SET(lets_credit, CREDIT_ENTROPY_YES_PLEASE, CREDIT_ENTROPY_YES_FORCED)) { + _cleanup_free_ struct rand_pool_info *info = NULL; + + info = malloc(offsetof(struct rand_pool_info, buf) + k); + if (!info) + return log_oom(); + + info->entropy_count = k * 8; + info->buf_size = k; + memcpy(info->buf, buf, k); + + if (ioctl(random_fd, RNDADDENTROPY, info) < 0) + return log_warning_errno(errno, "Failed to credit entropy, ignoring: %m"); + } else { + 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"); + } } } 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_and_chown(seed_fd, 0600, 0, 0); + bool getrandom_worked = false; - k = loop_read(random_fd, buf, buf_size, 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) - 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."); + 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(IN_SET(errno, ENOSYS, EOPNOTSUPP) ? LOG_DEBUG : LOG_WARNING, errno, + "Failed to mark seed file as creditable, ignoring: %m"); } - return r; + return 0; } DEFINE_MAIN_FUNCTION(run); |