linux-kernel - [PATCH 3.16 018/328] alarmtimer: Prevent overflow for relative nanosleep

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Message-ID: <lsq.1544392233.362384152@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
        "Team OWL337" <icytxw@...il.com>,
        "John Stultz" <john.stultz@...aro.org>
Subject: [PATCH 3.16 018/328] alarmtimer: Prevent overflow for relative
 nanosleep

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit 5f936e19cc0ef97dbe3a56e9498922ad5ba1edef upstream.

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 <icytxw@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: John Stultz <john.stultz@...aro.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1807020926360.1595@nanos.tec.linutronix.de
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/time/alarmtimer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -775,7 +775,8 @@ 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);
 	}
 
 	if (alarmtimer_do_nsleep(&alarm, exp))