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Commit 65cb24de authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Greg Kroah-Hartman
Browse files

posix-timers: Sanitize overrun handling 



[ Upstream commit 78c9c4dfbf8c04883941445a195276bb4bb92c76 ]

The posix timer overrun handling is broken because the forwarding functions
can return a huge number of overruns which does not fit in an int. As a
consequence timer_getoverrun(2) and siginfo::si_overrun can turn into
random number generators.

The k_clock::timer_forward() callbacks return a 64 bit value now. Make
k_itimer::ti_overrun[_last] 64bit as well, so the kernel internal
accounting is correct. 3Remove the temporary (int) casts.

Add a helper function which clamps the overrun value returned to user space
via timer_getoverrun(2) or siginfo::si_overrun limited to a positive value
between 0 and INT_MAX. INT_MAX is an indicator for user space that the
overrun value has been clamped.

Reported-by: default avatarTeam OWL337 <icytxw@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Link: https://lkml.kernel.org/r/20180626132705.018623573@linutronix.de


[florian: Make patch apply to v4.9.135]
Signed-off-by: default avatarFlorian Fainelli <f.fainelli@gmail.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent b0b77fb6

include/linux/posix-timers.h

+2 −2
Original line number Diff line number Diff line
@@ -65,8 +65,8 @@ struct k_itimer { 
	spinlock_t it_lock;

	clockid_t it_clock;		/* which timer type */

	timer_t it_id;			/* timer id */

	int it_overrun;			/* overrun on pending signal  */

	int it_overrun_last;		/* overrun on last delivered signal */

	s64 it_overrun;			/* overrun on pending signal  */

	s64 it_overrun_last;		/* overrun on last delivered signal */

	int it_requeue_pending;		/* waiting to requeue this timer */

#define REQUEUE_PENDING 1

	int it_sigev_notify;		/* notify word of sigevent struct */

kernel/time/posix-cpu-timers.c

+1 −1
Original line number Diff line number Diff line
@@ -103,7 +103,7 @@ static void bump_cpu_timer(struct k_itimer *timer, 
			continue;



		timer->it.cpu.expires += incr;

		timer->it_overrun += 1 << i;

		timer->it_overrun += 1LL << i;

		delta -= incr;

	}

}

kernel/time/posix-timers.c

+19 −10
Original line number Diff line number Diff line
@@ -355,6 +355,17 @@ static __init int init_posix_timers(void) 


__initcall(init_posix_timers);



/*

 * The siginfo si_overrun field and the return value of timer_getoverrun(2)

 * are of type int. Clamp the overrun value to INT_MAX

 */

static inline int timer_overrun_to_int(struct k_itimer *timr, int baseval)

{

	s64 sum = timr->it_overrun_last + (s64)baseval;



	return sum > (s64)INT_MAX ? INT_MAX : (int)sum;

}



static void schedule_next_timer(struct k_itimer *timr)

{

	struct hrtimer *timer = &timr->it.real.timer;
@@ -362,12 +373,11 @@ static void schedule_next_timer(struct k_itimer *timr) 
	if (timr->it.real.interval.tv64 == 0)

		return;



	timr->it_overrun += (unsigned int) hrtimer_forward(timer,

						timer->base->get_time(),

	timr->it_overrun += hrtimer_forward(timer, timer->base->get_time(),

					    timr->it.real.interval);



	timr->it_overrun_last = timr->it_overrun;

	timr->it_overrun = -1;

	timr->it_overrun = -1LL;

	++timr->it_requeue_pending;

	hrtimer_restart(timer);

}
@@ -396,7 +406,7 @@ void do_schedule_next_timer(struct siginfo *info) 
		else

			schedule_next_timer(timr);



		info->si_overrun += timr->it_overrun_last;

		info->si_overrun = timer_overrun_to_int(timr, info->si_overrun);

	}



	if (timr)
@@ -491,8 +501,7 @@ static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer) 
					now = ktime_add(now, kj);

			}

#endif

			timr->it_overrun += (unsigned int)

				hrtimer_forward(timer, now,

			timr->it_overrun += hrtimer_forward(timer, now,

						timr->it.real.interval);

			ret = HRTIMER_RESTART;

			++timr->it_requeue_pending;
@@ -633,7 +642,7 @@ SYSCALL_DEFINE3(timer_create, const clockid_t, which_clock, 
	it_id_set = IT_ID_SET;

	new_timer->it_id = (timer_t) new_timer_id;

	new_timer->it_clock = which_clock;

	new_timer->it_overrun = -1;

	new_timer->it_overrun = -1LL;



	if (timer_event_spec) {

		if (copy_from_user(&event, timer_event_spec, sizeof (event))) {
@@ -762,7 +771,7 @@ common_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting) 
	 */

	if (iv.tv64 && (timr->it_requeue_pending & REQUEUE_PENDING ||

			timr->it_sigev_notify == SIGEV_NONE))

		timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);

		timr->it_overrun += hrtimer_forward(timer, now, iv);



	remaining = __hrtimer_expires_remaining_adjusted(timer, now);

	/* Return 0 only, when the timer is expired and not pending */
@@ -824,7 +833,7 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_t, timer_id) 
	if (!timr)

		return -EINVAL;



	overrun = timr->it_overrun_last;

	overrun = timer_overrun_to_int(timr, 0);

	unlock_timer(timr, flags);



	return overrun;