[SRU][Trusty][PATCH v2 1/1] posix-timers: Sanitize overrun handling
Khalid Elmously
khalid.elmously at canonical.com
Wed Nov 28 05:19:31 UTC 2018
From: Thomas Gleixner <tglx at linutronix.de>
CVE-2018-12896
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 at gmail.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Acked-by: John Stultz <john.stultz at linaro.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Michael Kerrisk <mtk.manpages at gmail.com>
Link: https://lkml.kernel.org/r/20180626132705.018623573@linutronix.de
(backported from commit 78c9c4dfbf8c04883941445a195276bb4bb92c76)
Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
---
include/linux/posix-timers.h | 4 ++--
kernel/posix-cpu-timers.c | 8 ++++----
kernel/posix-timers.c | 31 ++++++++++++++++++++-----------
3 files changed, 26 insertions(+), 17 deletions(-)
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 907f3fd191ac..3e28a1a8d823 100644
--- 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/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c7f31aa272f7..0f62265a707c 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/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;
}
}
@@ -761,7 +761,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
~REQUEUE_PENDING;
timer->it_overrun_last = 0;
- timer->it_overrun = -1;
+ timer->it_overrun = -1LL;
if (new_expires != 0 && !(val < new_expires)) {
/*
@@ -1119,7 +1119,7 @@ out_unlock:
out:
timer->it_overrun_last = timer->it_overrun;
- timer->it_overrun = -1;
+ timer->it_overrun = -1LL;
++timer->it_requeue_pending;
}
@@ -1327,7 +1327,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
memset(&timer, 0, sizeof timer);
spin_lock_init(&timer.it_lock);
timer.it_clock = which_clock;
- timer.it_overrun = -1;
+ timer.it_overrun = -1LL;
error = posix_cpu_timer_create(&timer);
timer.it_process = current;
if (!error) {
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 26b910462a0c..8ef1ab65fe84 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -346,6 +346,17 @@ 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;
@@ -353,12 +364,11 @@ 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);
}
@@ -387,7 +397,7 @@ 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)
@@ -482,9 +492,8 @@ 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.real.interval);
+ timr->it_overrun += hrtimer_forward(timer, now,
+ timr->it.real.interval);
ret = HRTIMER_RESTART;
++timr->it_requeue_pending;
}
@@ -624,7 +633,7 @@ 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))) {
@@ -754,7 +763,7 @@ 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_THREAD_ID) == SIGEV_NONE))
- timr->it_overrun += (unsigned int) hrtimer_forward(timer, now, iv);
+ timr->it_overrun += hrtimer_forward(timer, now, iv);
remaining = ktime_sub(hrtimer_get_expires(timer), now);
/* Return 0 only, when the timer is expired and not pending */
@@ -816,7 +825,7 @@ 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;
--
2.17.1
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