posix-timers: Fix division by zero bug

BugLink: https://bugs.launchpad.net/bugs/1837257
commit 0e334db6bb4b1fd1e2d72c1f3d8f004313cd9f94 upstream.

The signal delivery path of posix-timers can try to rearm the timer even if
the interval is zero. That's handled for the common case (hrtimer) but not
for alarm timers. In that case the forwarding function raises a division by
zero exception.

The handling for hrtimer based posix timers is wrong because it marks the
timer as active despite the fact that it is stopped.

Move the check from common_hrtimer_rearm() to posixtimer_rearm() to cure
both issues.

Reported-by: syzbot+9d38bedac9cc77b8ad5e@syzkaller.appspotmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: sboyd@kernel.org
Cc: stable@vger.kernel.org
Cc: syzkaller-bugs@googlegroups.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1812171328050.1880@nanos.tec.linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 0f0e2566ef89c52d93da864d1a961b0569f07350..12d72c082286741e0a775f4b0da29d9772a8b89e 100644 (file)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -298,9 +298,6 @@ static void common_hrtimer_rearm(struct k_itimer *timr)
 {
        struct hrtimer *timer = &timr->it.real.timer;
 
-       if (!timr->it_interval)
-               return;
-
        timr->it_overrun += hrtimer_forward(timer, timer->base->get_time(),
                                            timr->it_interval);
        hrtimer_restart(timer);
@@ -326,7 +323,7 @@ void posixtimer_rearm(struct siginfo *info)
        if (!timr)
                return;
 
-       if (timr->it_requeue_pending == info->si_sys_private) {
+       if (timr->it_interval && timr->it_requeue_pending == info->si_sys_private) {
                timr->kclock->timer_rearm(timr);
 
                timr->it_active = 1;