time: Normalize timespec64 before timespec64_compare()

hulk inclusion
category: bugfix
bugzilla: 185831, https://gitee.com/openeuler/kernel/issues/I4MO2G
CVE: NA

-------------------------------------------------

Passing unnormalized timespec64 to timespec64_compare() may cause
incorrect results.

For example:
  wall_to_monotonic = {tv_sec = -10, tv_nsec = 900000000}
  ts_delta = {tv_sec = -9, tv_nsec = -900000000}

timespec64_compare() returns -1, but actually wall_to_monotonic > ts_delta.
This will cause wall_to_monotonic to become a positive number.

Use timespec64_sub() instead of direct subtraction to avoid this.
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NXiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/time64.h

@@ -62,6 +62,8 @@ static inline int timespec64_equal(const struct timespec64 *a,
  * lhs < rhs:  return <0
  * lhs == rhs: return 0
  * lhs > rhs:  return >0
+ *
+ * Note: Both lhs and rhs must be normalized.
  */
 static inline int timespec64_compare(const struct timespec64 *lhs, const struct timespec64 *rhs)
 {

kernel/time/timekeeping.c

@@ -1236,8 +1236,7 @@ int do_settimeofday64(const struct timespec64 *ts)
 	timekeeping_forward_now(tk);
 
 	xt = tk_xtime(tk);
-	ts_delta.tv_sec = ts->tv_sec - xt.tv_sec;
-	ts_delta.tv_nsec = ts->tv_nsec - xt.tv_nsec;
+	ts_delta = timespec64_sub(*ts, xt);
 
 	if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
 		ret = -EINVAL;