From d897a4ab11dc8a9fda50d2eccc081a96a6385998 Mon Sep 17 00:00:00 2001

From: Miroslav Lichvar <mlichvar@redhat.com>

Date: Tue, 18 Jun 2019 17:47:13 +0200

Subject: [PATCH] ntp: Limit TAI-UTC offset

Git-commit: d897a4ab11dc8a9fda50d2eccc081a96a6385998

Patch-mainline: v5.3-rc1

References: git-fixes

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: Frederic Weisbecker <fweisbecker@suse.com>

---

 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 8de4f789dc1b..65eb796610dc 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

@@ -691,7 +692,8 @@ static inline void process_adjtimex_modes(const struct __kernel_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)

-- 

2.34.1