ntpd: make NTP client and server Y2036/2038-ready

The 32-bit integer part of the NTP timestamp overflows in year 2036,
which starts the second NTP era.

Modify the timestamp conversion to shift values between 1900-1970 (in
the first era) to the second era to enable the client to measure its
offset correctly until year 2106 (assuming 64-bit time_t).

Also update the conversion from double used when stepping the clock to
work with 64-bit time_t after reaching the maximum 32-bit value in 2038
and the server conversion to work correctly in the next NTP era.

function                                             old     new   delta
lfp_to_d                                              51      64     +13
step_time                                            326     332      +6
.rodata                                           105260  105264      +4
d_to_lfp                                             100      86     -14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/1 up/down: 23/-14)              Total: 9 bytes

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/networking/ntpd.c b/networking/ntpd.c
index 204e1d7c2..4365166ff 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -554,7 +554,7 @@ gettime1900d(void)
 static void
 d_to_tv(struct timeval *tv, double d)
 {
-        tv->tv_sec = (long)d;
+        tv->tv_sec = (time_t)d;
         tv->tv_usec = (d - tv->tv_sec) * 1000000;
 }
 
@@ -565,6 +565,14 @@ lfp_to_d(l_fixedpt_t lfp)
         lfp.int_partl = ntohl(lfp.int_partl);
         lfp.fractionl = ntohl(lfp.fractionl);
         ret = (double)lfp.int_partl + ((double)lfp.fractionl / UINT_MAX);
+        /*
+         * Shift timestamps before 1970 to the second NTP era (2036-2106):
+         * int_partl value of OFFSET_1900_1970 (2208988800) is interpreted as
+         * the start of year 1970 and it is the minimal representable time,
+         * all values form the sequence 2208988800..0xffffffff,0..2208988799.
+         */
+        if (lfp.int_partl < OFFSET_1900_1970)
+                ret += (double)(1ULL << 32); /* because int_partl is 32-bit wide */
         return ret;
 }
 static NOINLINE double
@@ -582,8 +590,8 @@ d_to_lfp(l_fixedpt_t *lfp, double d)
 {
         uint32_t intl;
         uint32_t frac;
-        intl = (uint32_t)d;
-        frac = (uint32_t)((d - intl) * UINT_MAX);
+        intl = (uint32_t)(time_t)d;
+        frac = (uint32_t)((d - (time_t)d) * UINT_MAX);
         lfp->int_partl = htonl(intl);
         lfp->fractionl = htonl(frac);
 }