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[PATCH 06/11] ntp: Verify offset doesn't overflow in ntp_update_offset

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From: Sasha Levin <sasha.levin@oracle.com>

We need to make sure that the offset is valid before manipulating it,
otherwise it might overflow on the multiplication.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
[jstultz: Reworked one of the checks so it makes more sense]
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 kernel/time/ntp.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 149cc80..125fc03 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -297,15 +297,17 @@ static void ntp_update_offset(long offset)
 	if (!(time_status & STA_PLL))
 		return;
 
-	if (!(time_status & STA_NANO))
+	if (!(time_status & STA_NANO)) {
+		/* Make sure the multiplication below won't overflow */
+		offset = clamp(offset, -USEC_PER_SEC, USEC_PER_SEC);
 		offset *= NSEC_PER_USEC;
+	}
 
 	/*
 	 * Scale the phase adjustment and
 	 * clamp to the operating range.
 	 */
-	offset = min(offset, MAXPHASE);
-	offset = max(offset, -MAXPHASE);
+	offset = clamp(offset, -MAXPHASE, MAXPHASE);
 
 	/*
 	 * Select how the frequency is to be controlled
-- 
1.9.1

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[PATCH 00/11][GIT PULL] Timekeeping items for 4.5 John Stultz <john.stultz@linaro.org> - 2015-12-18 22:40 +0100
  [PATCH 07/11] time: Verify time values in adjtimex ADJ_SETOFFSET to avoid overflow John Stultz <john.stultz@linaro.org> - 2015-12-18 22:40 +0100
  [PATCH 06/11] ntp: Verify offset doesn't overflow in ntp_update_offset John Stultz <john.stultz@linaro.org> - 2015-12-18 22:40 +0100
  [PATCH 01/11] MAINTAINERS: Add entry for kernel/time/alarmtimer.c John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 09/11] ntp: Change time_reftime to time64_t and utilize 64bit __ktime_get_real_seconds John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 03/11] time: Avoid signed overflow in timekeeping_get_ns() John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 04/11] clocksource: Add CPU info to clocksource watchdog reporting John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 10/11] ntp: Fix second_overflow's input parameter type to be 64bits John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 08/11] timekeeping: Provide internal function __ktime_get_real_seconds John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 05/11] selftests/timers: fix write return value handlng John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100
  [PATCH 02/11] alarmtimer: Avoid unexpected rtc interrupt when system resume from S3 John Stultz <john.stultz@linaro.org> - 2015-12-18 22:50 +0100

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