[PATCH] time: Normalize timespec64 before timespec64_compare()

[PATCH] time: Normalize timespec64 before timespec64_compare()

[Yu Liao]

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: Yu Liao <liaoyu15@huawei.com>
---
 include/linux/time64.h    | 2 ++
 kernel/time/timekeeping.c | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/time64.h b/include/linux/time64.h
index 81b9686a2079..f74a36d253cd 100644
--- a/include/linux/time64.h
+++ b/include/linux/time64.h
@@ -50,6 +50,8 @@ 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)
 {
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index b348749a9fc6..dcdcb85121e4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1306,8 +1306,7 @@ 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;
-- 
2.25.1

Re: [PATCH] time: Normalize timespec64 before timespec64_compare()

[Yu Liao]

Is there any comments about this patch?
BTW, is it necessary to add set_normalized_timespec64 to timespec64_compare?

Thanks,
Yu

On 2021/12/2 21:07, Yu Liao wrote:
> 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: Yu Liao <liaoyu15@huawei.com>
> ---
>   include/linux/time64.h    | 2 ++
>   kernel/time/timekeeping.c | 3 +--
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/time64.h b/include/linux/time64.h
> index 81b9686a2079..f74a36d253cd 100644
> --- a/include/linux/time64.h
> +++ b/include/linux/time64.h
> @@ -50,6 +50,8 @@ 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)
>   {
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index b348749a9fc6..dcdcb85121e4 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1306,8 +1306,7 @@ 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;