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

From: Ben Hutchings
Date: Sun Dec 09 2018 - 17:26:39 EST

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


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1807020926360.1595@xxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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))