posix-timers: Fix division by zero bug

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>

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index bd62b5eeb5a057b000d6b8019072853b5daa37d6..31f49ae80f43dd76e5eea85416dc362b45e60780 100644 (file)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -289,9 +289,6 @@ 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);
@@ -317,7 +314,7 @@ void posixtimer_rearm(struct kernel_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;