ntp: Verify offset doesn't overflow in ntp_update_offset

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@oracle.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
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>

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 149cc8086aea..125fc0342355 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