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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.14 50/87] posix-timers: Sanitize overrun handling
Thread-Topic: [PATCH AUTOSEL 4.14 50/87] posix-timers: Sanitize overrun
 handling
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Date:   Mon, 17 Sep 2018 03:02:54 +0000
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From: Thomas Gleixner <tglx@linutronix.de>

[ 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: Team OWL337 <icytxw@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John 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
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 include/linux/posix-timers.h   |  4 ++--
 kernel/time/posix-cpu-timers.c |  2 +-
 kernel/time/posix-timers.c     | 31 ++++++++++++++++++++-----------
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 672c4f32311e..437a539898ae 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -82,8 +82,8 @@ struct k_itimer {
 	clockid_t		it_clock;
 	timer_t			it_id;
 	int			it_active;
-	int			it_overrun;
-	int			it_overrun_last;
+	s64			it_overrun;
+	s64			it_overrun_last;
 	int			it_requeue_pending;
 	int			it_sigev_notify;
 	ktime_t			it_interval;
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.=
c
index 5b117110b55b..2da660d53a4b 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -84,7 +84,7 @@ static void bump_cpu_timer(struct k_itimer *timer, u64 no=
w)
 			continue;
=20
 		timer->it.cpu.expires +=3D incr;
-		timer->it_overrun +=3D 1 << i;
+		timer->it_overrun +=3D 1LL << i;
 		delta -=3D incr;
 	}
 }
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index fb0935612d4e..55d45fe2cc17 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -283,6 +283,17 @@ static __init int init_posix_timers(void)
 }
 __initcall(init_posix_timers);
=20
+/*
+ * 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 =3D timr->it_overrun_last + (s64)baseval;
+
+	return sum > (s64)INT_MAX ? INT_MAX : (int)sum;
+}
+
 static void common_hrtimer_rearm(struct k_itimer *timr)
 {
 	struct hrtimer *timer =3D &timr->it.real.timer;
@@ -290,9 +301,8 @@ static void common_hrtimer_rearm(struct k_itimer *timr)
 	if (!timr->it_interval)
 		return;
=20
-	timr->it_overrun +=3D (unsigned int) hrtimer_forward(timer,
-						timer->base->get_time(),
-						timr->it_interval);
+	timr->it_overrun +=3D hrtimer_forward(timer, timer->base->get_time(),
+					    timr->it_interval);
 	hrtimer_restart(timer);
 }
=20
@@ -321,10 +331,10 @@ void posixtimer_rearm(struct siginfo *info)
=20
 		timr->it_active =3D 1;
 		timr->it_overrun_last =3D timr->it_overrun;
-		timr->it_overrun =3D -1;
+		timr->it_overrun =3D -1LL;
 		++timr->it_requeue_pending;
=20
-		info->si_overrun +=3D timr->it_overrun_last;
+		info->si_overrun =3D timer_overrun_to_int(timr, info->si_overrun);
 	}
=20
 	unlock_timer(timr, flags);
@@ -418,9 +428,8 @@ static enum hrtimer_restart posix_timer_fn(struct hrtim=
er *timer)
 					now =3D ktime_add(now, kj);
 			}
 #endif
-			timr->it_overrun +=3D (unsigned int)
-				hrtimer_forward(timer, now,
-						timr->it_interval);
+			timr->it_overrun +=3D hrtimer_forward(timer, now,
+							    timr->it_interval);
 			ret =3D HRTIMER_RESTART;
 			++timr->it_requeue_pending;
 			timr->it_active =3D 1;
@@ -524,7 +533,7 @@ static int do_timer_create(clockid_t which_clock, struc=
t sigevent *event,
 	new_timer->it_id =3D (timer_t) new_timer_id;
 	new_timer->it_clock =3D which_clock;
 	new_timer->kclock =3D kc;
-	new_timer->it_overrun =3D -1;
+	new_timer->it_overrun =3D -1LL;
=20
 	if (event) {
 		rcu_read_lock();
@@ -702,7 +711,7 @@ void common_timer_get(struct k_itimer *timr, struct iti=
merspec64 *cur_setting)
 	 * expiry time forward by intervals, so expiry is > now.
 	 */
 	if (iv && (timr->it_requeue_pending & REQUEUE_PENDING || sig_none))
-		timr->it_overrun +=3D (int)kc->timer_forward(timr, now);
+		timr->it_overrun +=3D kc->timer_forward(timr, now);
=20
 	remaining =3D kc->timer_remaining(timr, now);
 	/* Return 0 only, when the timer is expired and not pending */
@@ -789,7 +798,7 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_t, timer_id)
 	if (!timr)
 		return -EINVAL;
=20
-	overrun =3D timr->it_overrun_last;
+	overrun =3D timer_overrun_to_int(timr, 0);
 	unlock_timer(timr, flags);
=20
 	return overrun;
--=20
2.17.1