linux-kernel - [PATCH v2] ntp: Verify offset doesn't overflow in ntp_update

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Message-Id: <1449777095-21981-1-git-send-email-john.stultz@linaro.org>
Date:	Thu, 10 Dec 2015 11:51:34 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Richard Cochran <richardcochran@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: [PATCH v2] ntp: Verify offset doesn't overflow in ntp_update_offset

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

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

Cc: Sasha Levin <sasha.levin@...cle.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
[jstultz: Reworked one of the checks so it makes more sense]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
v2: Reworked the overflow clamp to make more sense.

 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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