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    Subject[PATCH 4.14 064/293] ntp: Limit TAI-UTC offset
    Date
    [ Upstream commit d897a4ab11dc8a9fda50d2eccc081a96a6385998 ]

    Don't allow the TAI-UTC offset of the system clock to be set by adjtimex()
    to a value larger than 100000 seconds.

    This prevents an overflow in the conversion to int, prevents the CLOCK_TAI
    clock from getting too far ahead of the CLOCK_REALTIME clock, and it is
    still large enough to allow leap seconds to be inserted at the maximum rate
    currently supported by the kernel (once per day) for the next ~270 years,
    however unlikely it is that someone can survive a catastrophic event which
    slowed down the rotation of the Earth so much.

    Reported-by: Weikang shi <swkhack@gmail.com>
    Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Prarit Bhargava <prarit@redhat.com>
    Cc: Richard Cochran <richardcochran@gmail.com>
    Cc: Stephen Boyd <sboyd@kernel.org>
    Link: https://lkml.kernel.org/r/20190618154713.20929-1-mlichvar@redhat.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/time/ntp.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
    index 4bb9b66338be..9288532f73c8 100644
    --- a/kernel/time/ntp.c
    +++ b/kernel/time/ntp.c
    @@ -43,6 +43,7 @@ static u64 tick_length_base;
    #define MAX_TICKADJ 500LL /* usecs */
    #define MAX_TICKADJ_SCALED \
    (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
    +#define MAX_TAI_OFFSET 100000

    /*
    * phase-lock loop variables
    @@ -640,7 +641,8 @@ static inline void process_adjtimex_modes(struct timex *txc,
    time_constant = max(time_constant, 0l);
    }

    - if (txc->modes & ADJ_TAI && txc->constant >= 0)
    + if (txc->modes & ADJ_TAI &&
    + txc->constant >= 0 && txc->constant <= MAX_TAI_OFFSET)
    *time_tai = txc->constant;

    if (txc->modes & ADJ_OFFSET)
    --
    2.20.1


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