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: 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
[florian: Make patch apply to v4.9.135]
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 62d44c1..e4b8678 100644 (file)
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -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 */

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 39008d7..21a27bb 100644 (file)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -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;
        }
 }

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index fc7c37a..0e6ed2e 100644 (file)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -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.real.interval);
+       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;