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From: Thomas Gleixner <>
To: LKML <>
Cc: Air Icy <>, John Stultz <>
Subject: [PATCH] alarmtimer: Prevent overflow for relative nanosleep
Date: Mon, 2 Jul 2018 09:34:29 +0200 (CEST)
Message-ID: <> (raw)

Air Icy reported:

  UBSAN: Undefined behaviour in kernel/time/alarmtimer.c:811:7
  signed integer overflow:
  1529859276030040771 + 9223372036854775807 cannot be represented in type 'long long int'
  Call Trace:
   alarm_timer_nsleep+0x44c/0x510 kernel/time/alarmtimer.c:811
   __do_sys_clock_nanosleep kernel/time/posix-timers.c:1235 [inline]
   __se_sys_clock_nanosleep kernel/time/posix-timers.c:1213 [inline]
   __x64_sys_clock_nanosleep+0x326/0x4e0 kernel/time/posix-timers.c:1213
   do_syscall_64+0xb8/0x3a0 arch/x86/entry/common.c:290

alarm_timer_nsleep() uses ktime_add() to add the current time and the
relative expiry value. ktime_add() has no sanity checks so the addition
can overflow when the relative timeout is large enough.

Use ktime_add_safe() which has the necessary sanity checks in place and
limits the result to the valid range.

Fixes: 9a7adcf5c6de ("timers: Posix interface for alarm-timers")
Reported-by: Team OWL337 <>
Signed-off-by: Thomas Gleixner <>
 kernel/time/alarmtimer.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -808,7 +808,8 @@ static int alarm_timer_nsleep(const cloc
 	/* Convert (if necessary) to absolute time */
 	if (flags != TIMER_ABSTIME) {
 		ktime_t now = alarm_bases[type].gettime();
-		exp = ktime_add(now, exp);
+		exp = ktime_add_safe(now, exp);
 	ret = alarmtimer_do_nsleep(&alarm, exp, type);

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Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-02  7:34 Thomas Gleixner [this message]
2018-07-02  9:38 ` [tip:timers/core] " tip-bot for Thomas Gleixner

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