[patch] ntp: avoid integer overflow in do_adjtimex()

[Ingo Molnar <mingo@elte.hu>]

* Thomas Gleixner <tglx@linutronix.de> wrote:

> Here you go. It's ugly, but it should do the trick for now.
> 
> 	tglx

here's your patch with proper metadata:

--------------------->
From: Thomas Gleixner <tglx@linutronix.de>
Subject: [patch] ntp: avoid integer overflow in do_adjtimex()

John Stultz traced back ntpd problems to the following issue: 
do_adjtimex() [used by ntpd] can overflow if there's a too long delay 
between timer interrupts - as it can happen on NO_HZ. Expand the 
time_adjust calculation/division from 32 bits to 64 bits.

Found-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
Index: linux-2.6/kernel/time/ntp.c
===================================================================
--- linux-2.6.orig/kernel/time/ntp.c
+++ linux-2.6/kernel/time/ntp.c
@@ -196,7 +196,7 @@ void __attribute__ ((weak)) notify_arch_
  */
 int do_adjtimex(struct timex *txc)
 {
-	long mtemp, save_adjust;
+	long mtemp, save_adjust, rem;
 	s64 freq_adj, temp64;
 	int result;
 
@@ -314,7 +314,9 @@ int do_adjtimex(struct timex *txc)
 		    freq_adj += time_freq;
 		    freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 		    time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
-		    do_div(time_offset, NTP_INTERVAL_FREQ);
+		    time_offset = div_long_long_rem_signed(time_offset,
+							   NTP_INTERVAL_FREQ,
+							   &rem);
 		    time_offset <<= SHIFT_UPDATE;
 		} /* STA_PLL */
 	    } /* txc->modes & ADJ_OFFSET */