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ntp: Limit TAI-UTC offset

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[ 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>
This commit is contained in:
Miroslav Lichvar 2019-06-18 17:47:13 +02:00 committed by Greg Kroah-Hartman
parent 8d8f0b9009
commit d86c0b73f7
1 changed files with 3 additions and 1 deletions
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4
kernel/time/ntp.c
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@ -43,6 +43,7 @@ static u64 tick_length_base;
#define MAX_TICKADJ 500LL /* usecs */ #define MAX_TICKADJ 500LL /* usecs */
#define MAX_TICKADJ_SCALED \ #define MAX_TICKADJ_SCALED \
(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ) (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
#define MAX_TAI_OFFSET 100000
/* /*
* phase-lock loop variables * phase-lock loop variables
@ -698,7 +699,8 @@ static inline void process_adjtimex_modes(const struct timex *txc, s32 *time_tai
time_constant = max(time_constant, 0l); 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; *time_tai = txc->constant;
if (txc->modes & ADJ_OFFSET) if (txc->modes & ADJ_OFFSET)