diff options
Diffstat (limited to 'src/timesync')
| -rw-r--r-- | src/timesync/timesyncd-manager.c | 35 | ||||
| -rw-r--r-- | src/timesync/timesyncd-manager.h | 1 |
2 files changed, 16 insertions, 20 deletions
diff --git a/src/timesync/timesyncd-manager.c b/src/timesync/timesyncd-manager.c index 4352858..23480d4 100644 --- a/src/timesync/timesyncd-manager.c +++ b/src/timesync/timesyncd-manager.c @@ -25,6 +25,7 @@ #include "network-util.h" #include "ratelimit.h" #include "resolve-private.h" +#include "random-util.h" #include "socket-util.h" #include "string-util.h" #include "strv.h" @@ -77,13 +78,6 @@ static double ts_to_d(const struct timespec *ts) { return ts->tv_sec + (1.0e-9 * ts->tv_nsec); } -static uint32_t graceful_add_offset_1900_1970(time_t t) { - /* Adds OFFSET_1900_1970 to t and returns it as 32bit value. This is handles overflows - * gracefully in a deterministic and well-defined way by cutting off the top bits. */ - uint64_t a = (uint64_t) t + OFFSET_1900_1970; - return (uint32_t) (a & UINT64_C(0xFFFFFFFF)); -} - static int manager_timeout(sd_event_source *source, usec_t usec, void *userdata) { _cleanup_free_ char *pretty = NULL; Manager *m = ASSERT_PTR(userdata); @@ -125,20 +119,22 @@ static int manager_send_request(Manager *m) { } /* - * Set transmit timestamp, remember it; the server will send that back - * as the origin timestamp and we have an indication that this is the - * matching answer to our request. - * - * The actual value does not matter, We do not care about the correct - * NTP UINT_MAX fraction; we just pass the plain nanosecond value. + * Generate a random number as transmit timestamp, to ensure we get + * a full 64 bits of entropy to make it hard for off-path attackers + * to inject random time to us. */ - assert_se(clock_gettime(CLOCK_BOOTTIME, &m->trans_time_mon) >= 0); - assert_se(clock_gettime(CLOCK_REALTIME, &m->trans_time) >= 0); - ntpmsg.trans_time.sec = htobe32(graceful_add_offset_1900_1970(m->trans_time.tv_sec)); - ntpmsg.trans_time.frac = htobe32(m->trans_time.tv_nsec); + random_bytes(&m->request_nonce, sizeof(m->request_nonce)); + ntpmsg.trans_time = m->request_nonce; server_address_pretty(m->current_server_address, &pretty); + /* + * Record the transmit timestamp. This should be as close as possible to + * the send-to to ensure the timestamp is reasonably accurate + */ + assert_se(clock_gettime(CLOCK_BOOTTIME, &m->trans_time_mon) >= 0); + assert_se(clock_gettime(CLOCK_REALTIME, &m->trans_time) >= 0); + len = sendto(m->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &m->current_server_address->sockaddr.sa, m->current_server_address->socklen); if (len == sizeof(ntpmsg)) { m->pending = true; @@ -456,9 +452,8 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re m->missed_replies = 0; - /* check our "time cookie" (we just stored nanoseconds in the fraction field) */ - if (be32toh(ntpmsg.origin_time.sec) != graceful_add_offset_1900_1970(m->trans_time.tv_sec) || - be32toh(ntpmsg.origin_time.frac) != (unsigned long) m->trans_time.tv_nsec) { + /* check the transmit request nonce was properly returned in the origin_time field */ + if (ntpmsg.origin_time.sec != m->request_nonce.sec || ntpmsg.origin_time.frac != m->request_nonce.frac) { log_debug("Invalid reply; not our transmit time. Ignoring."); return 0; } diff --git a/src/timesync/timesyncd-manager.h b/src/timesync/timesyncd-manager.h index e595c7d..e9b5af5 100644 --- a/src/timesync/timesyncd-manager.h +++ b/src/timesync/timesyncd-manager.h @@ -71,6 +71,7 @@ struct Manager { /* last sent packet */ struct timespec trans_time_mon; struct timespec trans_time; + struct ntp_ts request_nonce; usec_t retry_interval; usec_t connection_retry_usec; bool pending; |