[tip:timers/core] alarmtimer: Prevent overflow for relative nanosleep

From: tip-bot for Thomas Gleixner
Date: Mon Jul 02 2018 - 05:38:16 EST

Commit-ID: 5f936e19cc0ef97dbe3a56e9498922ad5ba1edef
Gitweb: https://git.kernel.org/tip/5f936e19cc0ef97dbe3a56e9498922ad5ba1edef
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Mon, 2 Jul 2018 09:34:29 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 2 Jul 2018 11:33:26 +0200

alarmtimer: Prevent overflow for relative nanosleep

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

kernel/time/alarmtimer.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 78a3cc555823..fa5de5e8de61 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -808,7 +808,8 @@ static int alarm_timer_nsleep(const clockid_t which_clock, int flags,
/* 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);