The following commit has been merged into the timers/urgent branch of tip:

Commit-ID: 4e8c11b6b3f0b6a283e898344f154641eda94266 Gitweb: https://git.kernel.org/tip/4e8c11b6b3f0b6a283e898344f154641eda94266 Author: Yu Liao liaoyu15@huawei.com AuthorDate: Mon, 13 Dec 2021 21:57:27 +08:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Fri, 17 Dec 2021 23:06:22 +01:00

timekeeping: Really make sure wall_to_monotonic isn't positive

Even after commit e1d7ba873555 ("time: Always make sure wall_to_monotonic isn't positive") it is still possible to make wall_to_monotonic positive by running the following code:

int main(void) { struct timespec time;

clock_gettime(CLOCK_MONOTONIC, &time); time.tv_nsec = 0; clock_settime(CLOCK_REALTIME, &time); return 0; }

The reason is that the second parameter of timespec64_compare(), ts_delta, may be unnormalized because the delta is calculated with an open coded substraction which causes the comparison of tv_sec to yield the wrong result:

wall_to_monotonic = { .tv_sec = -10, .tv_nsec = 900000000 } ts_delta = { .tv_sec = -9, .tv_nsec = -900000000 }

That makes timespec64_compare() claim that wall_to_monotonic < ts_delta, but actually the result should be wall_to_monotonic > ts_delta.

After normalization, the result of timespec64_compare() is correct because the tv_sec comparison is not longer misleading:

wall_to_monotonic = { .tv_sec = -10, .tv_nsec = 900000000 } ts_delta = { .tv_sec = -10, .tv_nsec = 100000000 }

Use timespec64_sub() to ensure that ts_delta is normalized, which fixes the issue.

Fixes: e1d7ba873555 ("time: Always make sure wall_to_monotonic isn't positive") Signed-off-by: Yu Liao liaoyu15@huawei.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20211213135727.1656662-1-liaoyu15@huawei.com --- kernel/time/timekeeping.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index b348749..dcdcb85 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;